Ex post facto doesn't prevent the government from making something illegal and imposing punishment. It just prevents the government from retroactively making you a criminal for that once-legal possession/activity.
I explained it better on another forum: The government has and still can state that something that was once legal to possess, is no longer legal to possess. What they cannot do is say you broke the (new) law in the past, therefore you're a criminal even though that item/activity was legal at the time. Retroactive enforcement.
For example, MDMA was not restricted until 1985. The garbage sack full of molly you made the day before the drug became Schedule I isn't legal to own, sell, or distribute...but the government can't put you in jail for making it before that date.
And sure, I am well aware that these 2A-related restrictions are all unconstitutional. But waving ex post facto around like it will make the ATF's rule change go away is a waste of time and effort. Go after the meat of the change, not the process.
You are using “government” a bit loosely here.
The issue isn’t making something illegal going forward when it was legal in the past.
The issue is that it’s *congress*, not an executive branch agency, (like the ATF) that has the power to pass laws.
Since ATF lacks that authority, the agency (and the court) must apply the rule of lenity prior to using Chevron deference.
Chevron Deference works fine when both a) the statute is silent on the issue *and* b) the agency uses a reasonable construction of statute to make its interpretation. ATF appropriately used Chevron deference to determine bump stocks, braced pistols and forced reset triggers were legal.
Even though many of us felt they were missing the larger intent of the statute in all three interpretations, ATF was within its rights under administrative law and Chevron deference to do so because:
- they were issues the original law had not directly considered and was thus silent on; and
- (under a narrow read of the law) the ATF could argue their interpretations were a reasonable construction of the statute.
However, when criminal penalties are involved and would be imposed, the agency and the court must use an available valid interpretation most favorable to the defendant.
Given that ATF said for years that bump stocks, pistol braces and forced reset triggers were all legal, it can’t now argue there is *not* a valid interpretation under which those items are legal under existing law.
In short, Congress could in fact pass a law saying they are illegal to make or possess going forward - but the ATF cannot.