I think that Bush will win by 4%-5%, and will have in excess of 300 Electoral Votes. Even if he does, we'll have litigation that must be resolved by the Supreme Court. However, there is always a chance that Lurch could win. So, here's my scenario (take note, HM, I'll stand behind what I say now):
1) Regardless of the Presidential race, the Republicans will pick up 2-3 Senate seats and about 10 House seats. Thus, if the Republicans want to stop anything that Kerry proposes, they'll be able to do so, except for Executive Orders and foreign policy-type decisions. Of course, this will require that the Republicans grow a collective pair of stones, but I think that being out of control of the Executive Branch will help to facilitate that result. Nonetheless, the federal judiciary will become far more Leftist, thereby continuing and even accelerating the marginalization of most of the Constitution.
2) There may be some slight increases in taxes, but there will be LOTS more regulation of all types. Look also for lots of additional legislation in the area of the environment, and look for actual or threatened litigation to effectively control several industries (oil, guns, possibly drugs). Look for thousands of doctors to be leaving practice, as the regulatory stranglehold on medicine will grow tighter, driving down physician compensation. We won't be doing much additional drilling for oil (forget ANWR) or making any new refineries (still - we haven't done this since the late 1960's), so the price of oil and gas will remain high. Look for subsidies for solar energy, conservation and fuel cells.
3) Regarding guns, I am quite pessimistic. The Brady Bunch and their fellow travelers have been uniquely ineffective for the last 4 years because of who was in the White House. Kerry was right in asserting that Bush could've lobbied for the renewal of the AWB (and I'm damned glad that he didn't) - which is exactly what Kerry will do. I agree with MBane666 that he'll have to show dramatic "progress" somewhere, and since he'll have a decided lack of that domestically, we gunowners will be a big fat juicy target. After all, how many people own ARs, AKs, etc., and how many of them are very involved politically? We are, let's face it, an easy group to demonize, and most Republicans in office don't give enough of a damn about gun owners to put up with the public ridicule and accusations. Here's my list of coming restrictions:
a) The AWB will be back, bigger & badder. The list of banned guns will be longer, the list of permitted restricted features will be down to 1 of the 5 for semi-autos, instead of 2. Kiss your newly-produced semi-auto guns goodbye. Mags will once again be limited to 10. All of this will be PERMANENT, so that getting rid of it will be very much more difficult. It is POSSIBLE that a new AWB will have a grandfather clause, requiring registration. That won't go over well, and will have 90% plus non-compliance, but it will be on the books nonetheless. Look for such a thing if there's a massacre of schoolkids with a "permitted" version of a banned semi-auto.
b) .50 cal. guns will be either outlawed or treated as NFA guns on a national level.
c) Kiss gun shows and private transfers goodbye. All you need for that to pass the House and Senate by 99%-1% majorities will be one Beslan-type incident. Hell, such an incident could be used to justify an outright confiscation of semi-autos, but I WON'T predict that (but under President Hitlery I would).
d) Further restrictions/higher costs for FFL's, severely reducing the number out there (thus reducing competition and increasing prices - and insidiously reducing gun ownership by pricing more people out of the market). Possible disappearance of the C&R license, especially if some politician is whacked with a 75-year-old "weapon of war."
e) Possible restrictions or big taxes on the sale of smokeless powder or primers (either one will kill reloading).
I doubt that Kennedy and Kerry will be able to get almost all centerfire ammo effectively banned, but they'll use the threat of trying it to obtain something else (like the ban on private transfers). Once we swallow all of that, more will come, though it may have to wait for a different President.
4) Foreign and defense policy - here will be the real disaster. Kerry's mere election will embolden terrorists and nations that wish to see us at least taken down a peg. We'll end up pulling out of Iraq like we did in Vietnam, because even though Kerry will try to stay there for a while (to show how tough he is), the knowledge that we're leaving will cause many attacks on our troops, hastening the exit. The only other country besides England that will stick with us will be Israel, and the terrorists and the nations that support them will grow stronger. Look for at least one massive attack on US soil within a year after Kerry takes office - and be guaranteed that he, the rest of the Dems and the MSM blame Bush for it.
China will become an increasing threat, especially as Kerry begins to propose cuts to future weapons systems. After a couple of years of cuts, the Republicans will do what they did in the late '70's - add stuff into the budget that the President doesn't want.
2008 will be an interesting political year, just as 1980 was. Probably the results will be similar - because the public can elect freaks like Carter and Kerry, but we can't keep them around for very long.
5) Look for a number of 1sts from the First Lady, including telling some foreign leader that he's an @sshole.