The "gun show loophole" is their cherished Gun Control Act of 1968 working exactly as was (then) intended. Its intent was described as outlawing the sale of firearms in interstate commerce to individuals.
If you were a commercial dealer, you got your inventory often from out of state distributors. To continue to do this, you now needed a special license from the (then) ATF.
All of this was "hung" on the Interstate Commerce Clause. Sales between individuals of the same state were not affected because there was no possible way the transactions could be considered "interstate commerce".
Now what the gun grabbers are saying is that the law never meant what it said, and they are going to correct that "loophole". You can sell your books, computer, or car to anyone you want, and it's not considered interstate commerce. But they want to redefine guns to be items that never can leave the stream of interstate commerce, and so are always susceptible to meddling by the federal government.
To politicians, guns occupy a place of far more importance than artwork, gold, or financial instruments. They are in a class of their own, demanding special "attention".
Yes, just like ballots. A special threat to politicians.