WASHINGTON - A day after the deadliest shooting in U.S. history, Democrats challenged Sen. Pat Toomey (R., Pa.) to take a stronger stand on gun laws, aiming to undercut one of his prime arguments for reelection.

His Democratic challenger, Katie McGinty, hammered Toomey for voting last year to block a bill that would have barred suspected terrorists from buying guns. And Senate Democrats vowed to bring the politically charged measure back for another vote.

"Pat Toomey has worked to allow suspected terrorists to buy guns in this country, and that is just an outrageous position," said McGinty, who is challenging Toomey in one of the country's most critical Senate races. "Of all the kinds of tough issues, this one should not be a tough call."

Her comments Monday came hours after Senate Democrats pledged a renewed push on gun laws, starting with their proposal to ban purchases by anyone on federal terror watch lists.

"Are we going to take the painfully obvious commonsense steps and make sure terrorists can't get guns, or are we going to bow down to the NRA?" Sen. Chuck Schumer (D., N.Y.) asked in a conference call with reporters.

While the Democrats' bill appears to have little chance in the GOP-controlled Senate, another vote would highlight the sharp divide between the parties on guns - and could be especially potent in the Pennsylvania race, one of a handful that could determine control of the Senate.

Gun laws have become a political flash point for Toomey since he became the sole Republican to cosponsor a 2013 bill to expand background checks on gun buyers - a measure that fell short in the Senate but that he has featured heavily in campaign advertising.

He supported that plan in response to the Sandy Hook school massacre in Newtown, Conn., winning national praise and later touting it as a symbol of his bipartisan credentials. But Democrats have tried to undercut Toomey on the issue, questioning his commitment to the bill.

Toomey has not reintroduced the 2013 plan and, unlike some of his other top priorities, rarely brings it up on the Senate floor. He has, however, reiterated his support for broader background checks (usually when Democrats raise the issue), and last year gave a high-profile speech on it while accepting an honor from families of Sandy Hook victims.

His office did not say Monday how he would vote on the antiterror gun bill that Democrats are pressing again.

Instead, a spokeswoman pointed to his support for broader background checks "to keep guns out of the hands of people who shouldn't have them," while also calling for action to combat "violent Islamist extremism."

In response to McGinty's criticism, Toomey's campaign blasted her on a separate issue - so-called sanctuary cities - and said Toomey "led the bipartisan fight to strengthen background checks on gun purchases."

McGinty, in an interview, accused Toomey of doing too little to persuade his GOP colleagues to support the background-check plan.

"He lent his name to a bill, did little or nothing three years ago to try to get it passed, [and] since then has done absolutely nothing other than disavow any attempt to move on the legislation," she said.

In December, in the aftermath of a mass shooting in San Bernardino, Calif., Toomey and all but one other Senate Republican blocked Democrats' first attempt to bar terrorism suspects from buying guns.

At that time, he said it "makes sense" to stop people on terror watch lists from buying guns, but was concerned that the bill from Sen. Dianne Feinstein (D., Calif.) might infringe on the Second Amendment rights of people who are on federal watch lists due to an error.

Toomey instead supported a less-stringent GOP alternative that would have allowed the attorney general to stop suspected terrorists from buying guns - but only for 72 hours, unless the government could get a court order.

Republicans said that would give gun buyers due process, but Democrats derided it as a toothless political cover, saying lawyers could easily tie up a case for 72 hours, allowing the sale to go through.

The battle in Pennsylvania came as arguments on guns once again echoed from the White House to the presidential campaign trail to Senate and House races, but with few signs that this debate would end any differently than those that followed other mass shootings.

As he had vowed to do in the hours after the Orlando massacre, Sen. Robert P. Casey Jr. (D., Pa.) on Monday introduced a bill to ban anyone convicted of misdemeanor hate crimes from buying guns, though it wasn't immediately clear if that plan will get a vote in the new Democratic push.

"If you have proven you will commit criminal acts based on hate, you absolutely should not have access to a gun," Casey said in a news release. "It is time we as members of Congress do something."

McGinty embraced that plan, as well as renewed Democratic calls to ban assault weapons. And she planned a Tuesday news conference to hit Toomey on the issue again.