After years in which there were no meaningful changes to U.S. policy on gun laws, it’s worth pausing to appreciate the fact that there’s been some modest signs of progress of late.

A measure to improve the National Instant Criminal Background Check System, for example, was included in last week’s spending bill. So, too, was a provision to expand federal research on gun violence, following more than two decades in which this research was practically halted.

And then there’s bump stocks, an after-market accessory gun owners can attach to semi-automatic rifles to make it fire faster. Donald Trump announced a new policy on bump stocks on Twitter the other day, but not before trying to blame his predecessor – because for this president, practically everything is about Barack Obama.

“Obama Administration legalized bump stocks. BAD IDEA. As I promised, today the Department of Justice will issue the rule banning BUMP STOCKS with a mandated comment period. We will BAN all devices that turn legal weapons into illegal machine guns.”

As is too often the case, Trump seems confused about the details of policies he claims to care about. In reality, whether the president understands this or not, the Obama administration didn’t “legalize” bump stocks. The devices were already legal and in the marketplace. What Obama administration officials actually concluded was that new restrictions on bump stocks would need to be approved by Congress, rather than through new regulations created by the executive branch.

The Democratic White House followed the law; congressional Republicans ignored legislative proposals on the issue; and bump stock sales continued.

Several years later, the Trump administration’s Justice Department came to the same conclusion and told policymakers that in order to ban bump stocks, Congress would need to pass new legislation. The difference is, while Obama followed the legal guidance, Trump is ignoring it.

As the New York Times reported on Friday afternoon, “Attorney General Jeff Sessions said on Friday that the Justice Department was proposing to ban so-called bump stocks through regulations rather than wait for Congress to act, a move that defies recommendations by federal law enforcement officials and could subject the department to litigation from gun rights groups.”

The Justice Department’s full statement on the new regulation was posted online on Friday.

So, when Trump boasts that he’s banning these devices, what he means is that he’s advancing a legally suspect policy that’s likely to struggle in the courts. If the lawyers are right and the measure fails in the judiciary, the president’s latest move will have been a waste of time – which could’ve been better spent urging Congress to do what the White House believes should be done.