Prospects for a bipartisan deal on gun control legislation have dimmed significantly as President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE and Democratic leaders appear to be far apart on the key issue of expanding background checks.

Republicans expect Trump to put forward a proposal addressing gun violence later this week, but Democrats predict it is likely to fall far short of what is needed and that they may not vote for it.

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Democrats are pressing Trump to agree to a gun control bill already approved by the House, but the president has yet to even signal support for a scaled-down background check bill sponsored by Sens. Joe Manchin Joseph (Joe) ManchinThe debate over the filibuster entirely misses the point Trump plans to pick Amy Coney Barrett to replace Ginsburg on court Day before Trump refused to commit to peaceful transition, Aaron Sorkin described how he would write election night MORE (D-W.Va.) and Pat Toomey Patrick (Pat) Joseph ToomeyAppeals court rules NSA's bulk phone data collection illegal Dunford withdraws from consideration to chair coronavirus oversight panel GOP senators push for quick, partial reopening of economy MORE (R-Pa.).

“I don’t think anyone thinks he’s going to endorse the Toomey bill, which is weaker than the House bill,” said a senior Democratic aide, expressing growing doubt on Capitol Hill that Trump will strike a bipartisan deal.

As a result, the likelihood that Congress will fail to take action on gun violence a month after a new spate of shootings across the country appears to be growing.

Republicans say the political momentum within their party to expand background checks suffered a blow last week when Democratic presidential candidate Beto O’Rourke declared, “hell yes, we’re going to take your AR-15s, your AK-47s” at Thursday’s primary debate.

It was a big moment for O’Rourke’s campaign, but it underscored long-standing arguments from gun rights proponents that Democratic efforts on gun control are really aimed at the confiscation of firearms.

“This rhetoric undermines and hurts bipartisan efforts to actually make progress on commonsense gun safety efforts, like expanding background checks,” Toomey, who has been at the center of Senate negotiations, warned Friday.

It’s still possible the two parties could agree on some lower-hanging measures.

White House officials last week floated the idea of a new smartphone app that would be connected to the National

Instant Criminal Background Check System, which could be used to conduct background checks for sales between individuals who are not licensed dealers.

But it will be difficult for Democrats to agree to that proposal if it is a high watermark of what can be accepted by Republicans.

Manchin dismissed the idea of the smartphone app.

“The app’s crazy, totally crazy,” he said, arguing that the National Instant Criminal Background Check System works well as it is. “We have something that’s not broken, and they want to fix it and throw something at it. To throw that into a bill would be wrong.”

Similarly, Democrats are signaling that just passing “red flag” legislation that would empower law enforcement officials to confiscate firearms from people judged to be dangerous is not enough.

Senate Minority Leader Charles Schumer Chuck SchumerPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' 3 reasons why Biden is misreading the politics of court packing Cruz blocks amended resolution honoring Ginsburg over language about her dying wish MORE (D-N.Y.) argued on the Senate floor Monday that without an expansion of background check requirements, even a person who had his or her firearm confiscated by the police could immediately purchase another one from an individual who is not a federally licensed dealer.

Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.), a key negotiator who has had discussions with Trump on gun control, told reporters that the president needed to give them an affirmative sign by the end of last week in order to keep momentum from dying in Congress.

“My worry is that the forces inside the White House that are representing the gun lobby may be prevailing,” Murphy told reporters Monday. “I think that’s a shame.”

“They told us we would hear back by Thursday and we didn’t hear anything on Thursday or Friday or Saturday or Sunday,” he added. “Silence is probably indicative that they’re not willing to move.”

Manchin also sounded a pessimistic note.

“I haven’t heard back from their staff,” said Manchin, who panned the idea of creating a new smartphone app to conduct background checks.

Senate Republican Whip John Thune John Randolph ThuneHouse to vote on resolution affirming peaceful transition of power Trump dumbfounds GOP with latest unforced error Senate passes resolution reaffirming commitment to peaceful transition of power MORE (S.D.) said Monday afternoon that Trump is still reviewing his options, and a senior Republican aide said the White House is expected to present a plan to GOP leaders later this week.

“I think they’re looking at that and a whole range of issues, but I don’t think they’ve come to any conclusions,”

Thune, who met with Trump last week, said when asked about the prospect of the president endorsing expanded background checks.

Still, as more days pass without progress, gun control advocates in the Senate are growing increasingly pessimistic.

“It’s typical of the president and his statements on controversial issues. He’s on the side of the American people until he’s on the side of the special interest,” said Senate Democratic Whip Dick Durbin Richard (Dick) Joseph DurbinThe Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Feinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Grand jury charges no officers in Breonna Taylor death MORE (Ill.).

Conservatives are already warning the White House and GOP leaders of a backlash from gun rights advocates if Trump endorses a proposal to expand background checks to all online and gun show sales, as envisioned by the Manchin-Toomey bill.

“If Republicans abandon the Second Amendment and demoralize millions of Americans who care deeply about Second Amendment rights, that could go a long way to electing a President Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE,” Sen. Ted Cruz Rafael (Ted) Edward CruzCrenshaw looms large as Democrats look to flip Texas House seat SCOTUS confirmation in the last month of a close election? Ugly The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' MORE (R-Texas) warned last week, referring to the liberal Massachusetts senator, who is running for president.

A senior Republican aide on Monday expressed skepticism that Trump will endorse legislation that would significantly expand background checks, such as the Manchin-Toomey bill or the universal background check measure passed by the House in February.

In a call on Sunday with Schumer and Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.), Trump made no commitment on the House bill, according to two officials familiar with the call.

Jordain Carney contributed.