WASHINGTON — Sen. Pat Toomey (R., Pa.) dismissed as "nonsense" Katie McGinty's charge that he "has worked to allow suspected terrorists to buy guns."

Asked Tuesday about his challenger's criticism in the aftermath of the Orlando mass shooting, Toomey's sharpest response was a dismissive exhale.

"I don't know where that nonsense comes from," he said, noting that he voted for a Republican bill last year that would have given the U.S. attorney general a 72-hour window to stop terror suspects from buying guns.

Democrats, however, assailed Toomey for voting last December against their version, which would have imposed stronger restrictions on gun purchases by anyone on federal terror watch lists.

Senate Democrats plan to bring that bill back for another politically-fraught vote — but Toomey said he would still oppose it, if it is the same as the earlier version. He and other Republicans worried that people placed on watch lists in error could be stripped of their Second Amendment rights.

"There's absolutely no due process, the attorney general can randomly put anyone on that they like and that is not a reasonable thing to do," Toomey said. "I'm in favor of making it as difficult as we can for terrorists to get guns, but people should have an ability to challenge their status on such a list."

His comments came as the Orlando shooting reignited the debate on gun laws, nationally and in Toomey's critical Senate race, one of the most contentious in the country.

While there appears to be little chance the Democrats' bill can pass, they hope to use the fight to draw a contrast with Republicans — while GOP leaders called it a "politically motivated" effort.

McGinty on Tuesday dismissed as "toothless cover" the Republican plan that Toomey previously supported. It would have would have let authorities stop a suspected terrorist from buying a gun for 72 hours, but required a court order to block the sale any longer.

"Pat Toomey voted against a bill that would have made it harder for terrorism suspects to buy guns," she said in Philadelphia at a City Hall press conference. "And now we're mourning deaths in yet another mass murder at the hands of someone the FBI repeatedly investigated for his ties to terror, someone who Pat Toomey evidently thought it was perfectly OK to allow to buy guns."

Toomey has been entwined in the gun debate since 2013, when he won widespread praise as the lead Republican behind a bill to expand background checks for gun buys. While that effort fell short, it has become a symbol of his bipartisan credentials, and a major piece of his reelection pitch.

Democrats say he has done too little to push the bill since. McGinty said the renewed push on the anti-terror bill would show if he can back up his talk.

"Pat Toomey has done more than just about any Senator to lead the fight to pass bipartisan gun safety legislation," said Toomey campaign spokesman Ted Kwong. He said McGinty would "encourage more terrorism" because of her support for the Iran nuclear deal and other policies.