Ok, how?
I am going to play Devil's Advocate as I am frustrated with calls for action that are devoid of strategy and tactics. An election cycle is coming where folks not committed to the RKBA will see the danger of MSRs, EBRs, MSSAs, assault weapons, assault rifles, - anything you want to call them. They fundamentally want to be safe at the mall, place of worship, school, etc. They are not really interested in Socialism, they don't want to control you (common cliches).
So the gun bans have appeal. Make the case why a 19 year old should have the ability to purchase a basically short barrel rifle and equip it with a 100 round magazine?
The ball is in your court for how we go on the offensive to win legally. Choir arguments and cliches are not useful to a person fearing for their safety.
To help the discussion along, I am posting Gallup's polling work on guns and many of these track responses over time.
https://news.gallup.com/poll/1645/guns.aspx
Like ATLDave, my professional opinion is not the same as my personal preferences. These are simply issues that you can bat back and forth if you like or dispute my take on it.
Part of the issue is that Democrats as their rural roots shrivel are more influenced by their new urban and minority constituencies which are more anti-gun than the general population. In reverse, as the silk stocking Republicans have largely vanished or became Democrats, the Republican base of rural and outer suburb white voters has become more pro-gun. The battlegrounds are the suburbs with folks that are less ideological and more policy outcome oriented.
The problem is what plays for votes in the Democratic presidential primaries may not be helpful in the General Election as each D. candidate has a reason to push the limit on gun control because party activists that vote in primaries and volunteer for campaigns are overwhelmingly in support of radical action. Officeholders are caught in the crossfire in the House and Senate because they have to put together constituencies in states that may not reflect whatever the national mood in deep blue states is. Right now divided control of the House and Senate along with a President allows each party to essentially virtue signal without much cost. Regardless of the rather slanted media agenda, voters that are single issue on gun rights or gun bans are rather scarce--instead it is simply one additional item to consider. Economy and war and peace/terrorism are always at the top of the list along with occasional spikes in a short term crisis of some sort with lower numbers reflecting other issues. Immigration for example is one such thing that ebbs and flows with some historical regularity. Misconduct in government is another.
Right now, despite the hysteria based on today's news amplified by party politics, the gun control battle resembles WWI trench warfare with each side coming up with gambits that work in a small theater but these offensive motions peter out nationally.
The gun rights side has successfully pushed CCW for personal safety and Americans by and large refuse to ban handguns. Witness the near misses in the NFA act which originally included handguns, the GCA of 1968 driven by handgun assassinations, and the majority American support in the late 50's and 60's for a total ban on handguns. Some minor successes include FOPA and preventing the AWB from coming back into effect. There is also accordance that there is an individual right to own firearms codified in the Constitution which tends to legitimate it in the view of the tepid.
The gun banning side, thwarted at the national level, has turned to state offenses and ratcheted up ridiculous laws that do nothing nor prevent gun tragedies as the Gilroy and other massacres in California including Fresno and the bar near San Diego indicate. This sort of thing works when the blues dominate state politics but increasingly frustrate national action because the failure of these can be fairly demonstrated in the more purple and red regions. Thus, the gun banners have had to cede temporary defeat on handgun bans and focus instead on magazine limits and the new boogeyman of "assault rifles" often accompanied by the high powered assault rifles. Here, because semi auto AR and AK pattern rifles are more an offensive weapon due to range, cost, ammo availability, and ease of shooting by prospective mass murderers.
Aside from the Las Vegas rabid dog murderer, few, if any, of these mass shooters are a member of the gun culture and if these firearms were not available or expensive to own, would turn to handguns, shotguns, etc. or other things of mass mayhem. This has been true of shootings in other countries (aside from terrorism) which have actually occurred in some of the countries at higher rates than the U.S.
But, it has been the wedge that gun banners want with the UBC in their minds providing a nice gun registry to grab guns and they have persuaded quite a few people unfamiliar with the realities of gun buying and selling to go along. A second is an AWB and capacity restrictions on magazines along with raising the age to 21 on long arms. Capacity restrictions appear reasonable to a lot of folks, including firearm owners, with the idea that you only need a couple of bullets to stop a threat. The same with 21 for long arms as we restrict drinking for example to those 21 and over.
The UBC's have also been sold on the near mythical evil gun show loophole when in essence UBC's would probably affect only a few, if any, of the mass murderers. The illegal gun market of unscrupulous sellers, a large supply of pre-existing firearms with no real way to trace their ownership, and willing buyers already exists. In addition, many of these individual mass murderers would have and have passed background checks even some that should not have (TX Church murderer and VaTech murderer) and straw buyers proliferate.
My guess is that the 21 year old requirement might actually have a slightly greater effect on reducing these killings as a disproportionate number of 18-21 males have been these type murderers and many may lack the connections in order to acquire firearms illegally. Creepy loners might have an issue with getting straw buyers due to their isolation and no connections with the underground urban illegal firearm network. I have no strong opinions either way as insufficient evidence exists, but laws restricting minors from firearm purchases probably have prevented some high school shootings. Whether this can be extrapolated to 18-21 yr olds is debateable.
Magazine capacity is one of those things where you have to balance the fact that very large capacity mags might actually decrease the toll as these are prone to jamming (100 mags etc. are not the epitome of reliability) but due to the fact that many of these shooters might not be as proficient at reloading might actually have a slight effect on reducing death tolls. Gunny's thread on guns criminals use and his note that higher caps and the number of shots has increased among criminals lend some credence to this. You can shoot an SKS using stripper clips or an M1 Rifle pretty doggone fast if you are trained, the typical mass murderer is not that person as most demonstrate the profile of life's losers. Trainers see enough problems on reloading, so forcing a mass murderer to do more reloads under pressure could theoretically reduce mayhem. This is one of those things that a firearms trainer could address more than I could based on their experiences.
Now we get to red flag laws--as a principle, we the gun community should not want firearms in the hands of criminals, chronic drug or alcohol abusers, or those committed to institutions with severe mental illness. There is a reason that each are lawfully banned from owning or possessing firearms and while there are a few absolutists that believe than any restriction is unconstitutional, they are unlikely to get much support from the general population, politicians, nor the courts. The great difficulty is how to restore rights to these populations without causing additional violence as each of these may not be a permanent condition so the justice may not be served with the current life long banning. Currently, pardons can restore most rights but those are rare and hard to get. Maybe that is sufficient but there is no current similar system to those long ago that were treated for mental illness involuntarily and are now well. Perhaps that is something we should include with pardons or some other restoration of rights process.
We now get to the hard cases where there is perhaps a long record of anti-social behavior (violent threats, drug abuse and possession, stalking, domestic abuse/violence allegations, or even dementia) that might have led to arrests but later either pled down cases, diverted to the juvenile justice system, or simply ignored/mishandled by law enforcement/the courts/the schools/ or the mental health systems. Odds are that most of these individuals will not commit mass mayhem but obviously to think and talk about doing such things on an extended basis significantly raises the risk that they will do something. Thus, is it fair to in effect, have a pre-crime panel decide that by background that this sort of individual might not be a good custodian of firearms either temporarily and/or permanently. This version of the movie Minority Report from Phillip Dick's short story, dealt with such issues albeit with mental powers not available to current humans.
Like involuntary committals for treatment of mental illness, we should rightfully worry about the degree of due process, how to reverse unjust or unfounded decisions, and what compensation should be available for recompense of errors. Who should pay is another issue. Some will take the viewpoint that our rights are so important that if some people die as that consequence, that is the price of freedom and will oppose these laws outright. Others might argue it depends on the specific legislation proposed as we should balance individual rights with public safety. Gun banners will basically propose broad based seizures of private firearms by government as a good precedent and some believe that any person with a gun is a prospective mass murderer.
A red flag law might have worked in the cases of the cases of VA Tech, the CO Movie, the FL high school, and perhaps the Fresno situation. Each of these situations had multiple people that reported fixations by the perpetrators on death, killing, violence, etc. A similar situation exists with domestic violence protective orders, some of these will work and some will not in preventing future domestic incidents depending on a whole host of factors. It is possible that a lot of false positives might be generated by new red flag laws which we already have some experience with the classic MWAG 911 or worse SWATTING type reports that the police are obligated to investigate but most of these are quickly resolved by minimal investigation by police to screen out the real threats from the false ones. So how do you craft such a law to minimize false positives but maximize the protection to society from potential mass murderers by denying them quick and easy tools to commit mass mayhem?
If we do such a thing, I would strongly advise following the involuntary commitment model of mental health where extensive due process is available through the process including state provided lawyers, appellate review, cross examination of witnesses, sworn testimony, making false statements to such a body as legally liable for the individual with civil and criminal penalties, no ex parte hearings, etc. Orders should preferably be from state general trial court judges and not the lower magistrate, justice of the peace, etc. level that so often rubberstamp orders.
State recompense for damages to property, legal representation, etc. should be provided if the state loses its case on appeal to a circuit judge. Washington State for example has this provision in case self defense is successfully invoked. The incentive to minimize false positives is that the state should have to pay if these are unfounded allegations and individuals who make false reports for malicious reasons should face civil and criminal penalties. This would tend to focus the attention of the enforcement apparatus to legitimate cases only at the risk that some might slip through.
I am personally leaving out the whole AWB thing as it depending on the particulars such as whether it tries to ban all semi-automatics that is probably a bridge too far for success or whether it has the rather stupid California version of featureless abominations which could conceivably pass in some way. The least objectionable would be the stupid former federal AWB but still pointless in stopping mass mayhem. The whole registry issue could come up as Alexander A suggests but anti-gunners might be wary of such as it might cause the machine gun registry to be reopened as a poison pill amendment. A simple ban is easier to sell politically.
FWIW, detractors of DJT are correct to notice that he is ambivalent at best on the 2A issue because of background and NYC influences which is no different than GWB, or GHWB in action. GWB supported in 2000 and later reinstating the AWB if Congress sent it to him. His father tore up his NRA card and instituted bans based on the sporting purposes language of gun laws. But, Trump's linkage of the crisis at the borders with the gun control legislation more or less makes it a poison pill for any "bipartisan" agreement to come together because Democrats for identity politics reasons cannot agree to any border enforcement at the current time.
Thus, we may very well see a bit of failure theater where each side gets to credit claim if that darn other party had not obstructed their virtuous and righteous policy proposals. Doing nothing in particular other than windbaggery allows playing to the peanut gallery and thrilling the faithful but not risking doing anything that would upset the status quo. I would suspect that both this would result probably serves the interests of both parties at present.
The Republicans would come up with some policies and linkages that the Dems cannot agree to and the Dems would do the same. Resolution same old, same old, with a few electoral losses in 2020 swinging on it. Democrats want gun control on the agenda because they believe it helps them, more Republicans want border security issues highlighted because they believe it helps them. Both issues could be perilous if either side lets their extremists push things. Polling indicates that more or less that both of the above assertions about agenda priorities are correct regarding the mushy middle.
This linkage coupled with the overreach of refusing presidential visits, the overheated rhetoric, fundraising, etc. by the Dems, especially the presidential candidates, also makes it more unlikely to come to a deal over it as time passes. McConnell's refusal to reconvene the Senate during the recess more or less means that Congress stays on recess for weeks yet to go and by then other events may happen during that time changing the national conversation. Only the future can tell.