CAPITOL HILL -- President Trump scrambled the partisan divide on guns on Wednesday, siding with Democrats on dramatically expanding background checks and raising the purchasing age for semi-automatic weapons.

"It doesn't make sense that I have to wait til I'm 21 to get a handgun but I can get this weapon at 18," Mr. Trump said. "I don't know. So I'm just curious as to what you're doing about it in your bill."

Sens. Joe Manchin, D-West Virginia, and Pat Toomey, R-Pennsylvania, said they didn't address it.

"You know why, because you're afraid of the NRA," Mr. Trump said.

"My reservation about it, frankly, is that the vast majority of 18, 19, 20 year olds in Pennsylvania who have a rifle or a shotgun, they're not a threat to anyone. They are law-abiding citizens," Toomey said.

Mr. Trump also clashed with Republicans -- including recent shooting victim Steve Scalise -- who argued gun owners need the right to carry concealed weapons across state lines.

"These are people by and large who are helping us stop crimes," Scalise said. "These are people who are well-trained who actually go out there and help prevent crimes."

"I'm with you, but let it be a separate bill," Mr. Trump said. "You'll never get this passed. If you add concealed carry to this you'll never get it passed."

He was less enthused about a ban on assault weapons.

"You know the problem, Diane, these aren't guns where you go into a store and someone hands you a gun," Mr. Trump said to Democratic Sen. Diane Feinstein.

"Oh no, you can go into a store and you can buy and AR-15," she replied. "You can buy a Tech 9. You can buy all these weapons."

Those weapons, he argued, should have been confiscated from the Florida shooter -- even if it meant skirting the law

"The police saw that he was a problem," Mr. Trump said. "They didn't take any guns away. Now that could have been policing. I think they should have taken them away anyway -- whether they had the right or not."

Now there's a bill to close one loophole in the background check system that should get a vote in the next couple of weeks. Whether Congress goes further and embraces universal background checks is really going to depend on whether Mr. Trump crusades for it and takes on a gun lobby that has long opposed that legislation. As for banning bump stocks, Mr. Trump insisted Wednesday that he is going to do that by executive order very soon, no legislation necessary.