[OneWingedShark]

But they said they wouldn’t seize guns from innocent, law-abiding, non-violent citizens.

Simple: pass a law making all gun-ownership illegal -- then they can claim that they aren't persecuting the law-abiding, but the law breaking.
It's really easy to see what they're thinking.

[TigersEye]

Exactly! A law-abiding citizen will promptly take all of his or her guns down to the government buy-back, thank them profusely for giving them pennies on the dollar for them and for bonus points wear something wool and say "baaa baaa baaa" while standing in line.

Everyone else will be Federal felons and probably suspect of being a domestic terrorist. Avoid coffee shops.

[45Auto]

Ex Post Facto:

Latin for "from a thing done afterward." Ex post facto is most typically used to refer to a criminal law that applies retroactively, thereby criminalizing conduct that was legal when originally performed. Two clauses in the US Constitution prohibit ex post facto laws: Art 1, § 9 and Art. 1 § 10. see, e.g. Collins v. Youngblood, 497 US 37 (1990) and California Dep't of Corrections v. Morales, 514 US 499 (1995).