As a Vermonter who has watched all this unfold perhaps I can add some information and perspective.
First some background. For the longest time Vermont was a conservative state with some of the least restrictive firearm regulations in the nation. On the rare occasions an anti-gun bill was proposed it never gained much traction, and often the bill’s sponsor saw their political career fade. But as with other states, the demographics and political leanings of some regions of the state changed over the years, and this was seen even more disproportionately in the state legislature. Still, the right governor or committee chairman in the right place at the right time blocked most gun bills and life went on. Complacency was the norm, even though the local and state gun-right groups gave warnings.
Two days after the 2018 Parkland shooting Vermont officials uncover a youth’s written plan and notes about steps taken to shoot up a school. The moderate Republican Governor is rattled and says all gun control measures on are the table. That was all the anti-gun legislators needed. They dusted off their various plans and things were pushed through by April. We ended up with UBCs (with some family exceptions), long gun purchases restricted to 21 and older (unless you had a hunter safety card), and magazine restrictions (10 rds for long guns, 15 rds for handguns). An important note is that magazines with capacities over these limits that were already in someone’s possession were grandfathered in and legal to possess and use. The fact that the law did not go into effect for 6 months meant that a huge number of magazines were being purchased out of state or online. Once the law went into effect you could not legally bring higher capacity mags into the state, nor were you allowed to possess mags that were obtained after the law went into effect. You can see what kind of muddled mess this could be from an enforcement standpoint. Two different 30 round mags, one purchased in 2017 and the other brought in from a neighboring state in 2019. One’s legal, one isn’t.
Meanwhile… a self-admitted white supremacist is harassing an African-American state legislator. Things escalate, but he keeps it just under the threshold for being able to be charged with anything. But he has firmly landed on the Attorney General’s radar. So when his ex-wife reports that he went to neighboring New Hampshire, bought some 30 rounds mags (with a credit card…), and brought them home, Vermont law enforcement was able to pull together a case. He says the law is unconstitutional and it works its way through the system to the Vermont Supreme Court. The California ruling was viewed as a positive sign, but unfortunately it didn’t work out that way.
As one pro-gun person said, this was not the test-case we wanted, but it is the one we got. Would it have been a different outcome if a competitive shooter moved to Vermont and wasn’t allowed to bring his higher capacity mags with him? Hard to say.
A final note. The same governor who signed the above noted gun bills subsequently vetoed a waiting period, stating that he thinks Vermont’s gun laws are now adequate to protect people. Which is good considering the number of gun bills being discussed and/or introduced. So a word of caution to those in other states who might say “Gun control—that will never happen here”. Incremental change over time combined with some sort of precipitating event can change things quickly.