President Trump on Tuesday weighed in on 3D-printed guns -- a day after eight US states sued the government for an emergency ban on blueprints for the potentially untraceable weapons.

"I am looking into 3D plastic guns being sold to the public. Already spoke to NRA, doesn't seem to make much sense!" the commander-in-chief said on Twitter.

He's right that the specific concept of "3D plastic guns being sold to the public" doesn't make much sense. 

Because that's not the issue that eight states (and DC) are suing about. They're suing because Trump's own administration allowed Defense Distributed to publish blueprints for 3D-printed guns on the internet, after which practically anyone with the right equipment can use make their own guns. Because it's not necessarily illegal in the US, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives, to produce your own guns.

And not just out of plastic, by the way. Because only a single component of a gun is generally regulated -- the so-called "lower receiver" that contains the trigger and magazine well -- people can just 3D print that one piece out of plastic and buy the other strong metal parts on the internet. 

Even an all-metal 3D printed gun is totally possible. Defense Distributed makes a computer-controlled mill known as the Ghost Gunner that can make untraceable lower receivers for semiautomatic rifles out of a block of aluminum.

These are the things that at least 21 US attorneys general are concerned about, and why nine of them decided to file suit against the US government. 

Not that it will necessarily stop the blueprints from spreading -- though Defense Distributed originally planned to publish them tomorrow, Aug. 1, the organization confirmed to CNET that they were actually published on Friday, July 27. We downloaded one, and according to the current counts at Defcad.com, over 20,000 such blueprints have been downloaded already.

The White House, NRA and Defense Distributed didn't immediately reply to requests for comment.

Also Tuesday morning, a number of members of Congress have banded together to challenge 3D-printed guns by potentially enacting new laws, including the Untraceable Firearms Act (PDF) and the 3D Printing Safety Act. Senators Blumenthal, Nelson, Markey, Schumer, Menendez and Reps. Cicilline and Moulton appear to be behind the legislation, and we'll have a story about that soon.