A law expanding background checks and "red flags" laws are on the table in the Senate after the August recess, Senate Majority Leader Mitch McConnell, R-Ky., said Thursday in a radio interview.

"Those are two items that for sure will be front and center as we see what we can come together on and pass" the Republican leader said on a Kentucky radio station, speaking about a bipartisan bill from Sens. Joe Manchin, D-Va., and Pat Toomey, R-Pa., which would expand background checks to cover online and gun show sales, and the so-called red flag law, legislation that allows courts and police to confiscate firearms from people who are believed to be a threat to themselves or others.

“But what we can't do, is fail to pass something. By just locking up, and failing to pass, that's unacceptable," McConnell said, marking a significant departure from his past handling of gun legislation in the wake of tragedies.

McConnell has been a fierce opponent of gun restrictions throughout his 35-year Senate career, consistently resisting calls for gun control measures after massacres and reaping the benefits of a close relationship with the National Rifle Association. After the Sandy Hook shooting, he campaigned on preventing further gun control measures; after the Las Vegas shooting that left 59 dead, he said it was "premature" to discuss legislation during an ongoing investigation.

McConnell on Thursday said that the president called him "anxious to get an outcome." But he poured cold water on Democrats' calls to cancel the recess and address the issue immediately, saying the proposals needed "discussions" before they were brought to the floor.

"If we did that, we'd just have people scoring points and nothing would happen," he said. "There has to be a bipartisan discussion here of what we can agree on. If we do it prematurely, it'll be another frustrating experience for all of us and the public."

Three deadly mass shootings in the span of a a little more than a week — in Gilroy, California; El Paso, Texas; and Dayton, Ohio — have drawn renewed attention to the issue of gun control, with activists, hundreds of mayors and Democratic lawmakers urging the Senate to return to the Capitol early from congressional recess to act.

More than 200 House Democrats wrote a letter to McConnell on Wednesday urging him to end the August recess and pass stricter gun control legislation. The Democratic-controlled House passed two background check measures in February.

The House Judiciary Committee is still discussing coming back early from the recess, sources tell NBC News, to work on legislation including "red flag" laws and a law that would prohibit the sale of firearms to people convicted of hate crimes.

House Speaker Nancy Pelosi penned a letter to President Donald Trump Thursday, asking that he call the Senate back to Washington if McConnell won't.

“Mr. President, we have an opportunity to work in a bipartisan way to pass gun violence prevention background checks. However, Leader Mitch McConnell, describing himself as the ‘grim reaper,’ has been an obstacle to taking any action," she wrote in a letter posted online.

Ohio Rep. Tim Ryan, one of more than a dozen Democrats running for the party's 2020 nomination, is on a six-stop “Caravan for Change” on Thursday from Ohio to Kentucky with the gun-control group Moms Demand Action. They’ll finish with a rally in Louisville — McConnell’s hometown — on Thursday evening.

Democratic Rep. Jackie Speier of California, a shooting survivor, said she expected House Democrats would even begin picketing the Senate in hopes of urging action.

The sparring Congressional leaders' remarks come as a top Republican advocating for background checks says the president is engaging with lawmakers on the bill.

Toomey told MSNBC that he has spoken with the president "several times this week" about passing his legislation.

“I am hopeful there’s a different atmosphere now. There's Republicans taking a second look at this idea of broadening background checks. The president is clearly engaged and interested,” Toomey told MSNBC’s Andrea Mitchell. “These are new dynamics, and I want to run with this and see if we can get to the consensus we need.”

Toomey and Manchin first put forth the legislation in 2013 in the wake of the massacre at Sandy Hook Elementary School in Newtown, Connecticut. The bill failed under opposition from conservatives and the National Rifle Association and has been stalled since.

While the president has publicly signaled interest in expanding background checks — tweeting that perhaps Republicans and Democrats could pair immigration reform and gun control together — he has also tempered expectations.

Hours after tweeting support for background checks, remarks at the White House included no mention of the law. And he told reporters Wednesday, as he departed the White House en route to Dayton and El Paso to visit with families of victims and meet with law enforcement, that when it comes to the will of Congress, "I can only do what I can do."

The NRA has already begun to fight the new push for gun control.

NRA chief executive Wayne LaPierre on Tuesday told Trump that expanding background checks would not be popular among the president’s supporters, a source familiar with the matter confirmed to NBC News. LaPierre put out a statement on Thursday reiterating the group’s opposition to gun control legislation.

“The inconvenient truth is this: the proposals being discussed by many would not have prevented the horrific tragedies in El Paso and Dayton,” he said.

But Toomey said he was optimistic.

"Most of the discussions I’ve had with the president have focused on background checks and the Manchin-Toomey legislation that would require background checks on all commercial sales," he said. "I think the president has a real interest in this."

Pressed on whether background checks would prevent future massacres, Toomey said Thursday, "There is no law that will be passed that will guarantee there will be no more massacres."

But background checks, he said, will help.