WASHINGTON — With mounting desperation, President Trump called on Republican lawmakers Monday to reverse his election loss to Joe Biden when Congress convenes for a joint session this week to confirm the Electoral College vote.

Trump’s unprecedented attempt to overturn the presidential election is splitting the Republican Party. Some Republican lawmakers backing Trump are rushing ahead, despite an outpouring of condemnation from current and former Republican officials warning the effort is undermining Americans’ faith in democracy. All 10 living former defense secretaries wrote in an op-ed article that “the time for questioning the results has passed.”

It’s unclear the extent to which Republican leaders in Congress will be able to control Wednesday’s joint session, which could drag into the night. Trump himself is whipping up crowds for a Wednesday rally near the White House.

Trump’s allies are taking up his unfounded claims of voter fraud. But according to a consensus of election officials in the states he’s disputing — as well his former Attorney General William Barr — there is no evidence of fraud that could change the election outcome. Officials who have control over elections in their states, including the Arizona and Georgia battlegrounds that Biden won, have certified those results as accurate and valid.

Of the more than 50 lawsuits the president and his allies have filed challenging results, nearly all have been dismissed or dropped. He’s also lost twice at the U.S. Supreme Court.

The effort to keep Trump in office is being led by Sens. Josh Hawley of Missouri and Ted Cruz of Texas, along with rank-and-file House members, some on the party’s fringe.

“Just got off the phone with @realDonaldTrump,” tweeted newly elected Rep. Marjorie Taylor Greene of Georgia, who is aligned with a conspiracy group backing Trump.

“He wants you to call your Rep & Senators TODAY, ALL DAY!” she tweeted Monday. “Don’t let Republicans be the Surrender Caucus!”

A coalition of senators and senators-elect have pledged to reject the results of the presidential election. Associated Press

Republican leaders were to confer privately to assess the days ahead, a defining period that will help shape the post-Trump era.

Both Hawley and Cruz are potential 2024 presidential contenders, vying for Trump’s base of supporters. Vice President Mike Pence, who is under pressure to tip the results for Trump, will be closely watched as he presides in a ceremonial role over Wednesday’s joint session. He “welcomes” the challenge to the election results, his top aide said.

On Monday, more current and former Republican officials rebuked the effort to upend the election.

Former Sen. John Danforth of Missouri offered sharp criticism of the attempt by Hawley and the others, an especially stinging statement since Danforth has long been a supporter of Hawley.

“Lending credence to Trump’s false claim that the election was stolen is a highly destructive attack,” Danforth, the 84-year-old three-term senator from St. Louis, said in a written statement. “It is the opposite of conservative; it is radical.”

Listen to the full recorded audio of President Trump’s phone call with Georgia’s election chief:

Two current Republican senators, Rob Portman of Ohio and Mike Lee of Utah, joined the growing number who now oppose the legislators’ challenge.

Portman said in a statement, “I cannot support allowing Congress to thwart the will of the voters.”

The U.S. Chamber of Commerce, the giant lobbying organization and virtual embodiment of the business establishment, said Monday that the electoral vote challenge “undermines our democracy and the rule of law and will only result in further division across our nation.”

Senate Majority Leader Mitch McConnell has tried to prevent his party from engaging in this battle. House Minority Leader Kevin McCarthy, a Trump ally, has declined to speak publicly on it.

So far, Trump has enlisted support from a dozen Republican senators and up to 100 House Republicans to challenge Biden’s 306-232 Electoral College win.

With Biden set to be inaugurated Jan. 20, Trump is intensifying efforts to prevent the traditional transfer of power.

On a call disclosed Sunday, Trump can be heard pressuring Georgia officials to “find” him more votes from the Nov. 3 election he lost in that state.

Biden has been muted in his response to Trump. Transition spokesman Mike Gwin dismissed the senators’ effort as a “stunt” that won’t change the fact that Biden will be sworn in in two weeks.

Speaker Nancy Pelosi, who convened a private call of House Democrats on Monday, said in a letter to colleagues that while there is “no doubt” of Biden’s victory, their job now “is to convince more of the American people to trust in our democratic system.”

The current challenge to the presidential election is on a scale unseen since the aftermath of the Civil War, though the typically routine process of confirming Electoral College votes has been hit with brief objections before. In 2017, several House Democrats challenged Trump’s win, but Biden, who presided at the time as the vice president, swiftly dismissed them to assert Trump’s victory.

States run their own elections, and Congress has been loath to interfere. Despite Trump’s objections, many states adapted to the coronavirus pandemic by allowing more mail voting to ease health risks of voting in person.

“The 2020 election is over,” said a statement Sunday from a bipartisan group of 10 senators, including Republicans Susan Collins of Maine, Lisa Murkowski of Alaska, Bill Cassidy of Louisiana and Mitt Romney of Utah.

Republican Sen. Tom Cotton of Arkansas, another potential 2024 presidential hopeful, announced he, too, would not oppose the counting of certified electoral votes.

A range of Republican officials, including Gov. Larry Hogan of Maryland; Rep. Liz Cheney of Wyoming, the third-ranking House Republican leader; and former House Speaker Paul Ryan, have criticized the Republican efforts to overturn the election.

“The scheme by members of Congress to reject the certification of the presidential election makes a mockery of our system and who we are as Americans,” Hogan said in a statement Sunday.

Hawley defended his actions in a lengthy email over the weekend to colleagues, saying his Missouri constituents have been “loud and clear” in insisting Biden’s defeat of Trump was unfair.

Hawley plans to object to the state tally from Pennsylvania, although that state’s Republican senator, Pat Toomey, has said the results naming Biden the winner are valid.

Cruz’s coalition of 11 Republican senators vows to reject the Electoral College tallies unless Congress launches a commission to immediately conduct an audit of the election results. Congress is unlikely to agree to that.

The group, which presented no new evidence of election problems, includes Sens. Ron Johnson of Wisconsin, James Lankford of Oklahoma, Steve Daines of Montana, John Kennedy of Louisiana, Marsha Blackburn of Tennessee, Mike Braun of Indiana, Cynthia Lummis of Wyoming, Roger Marshall of Kansas, Bill Hagerty of Tennessee and Tommy Tuberville of Alabama.

Associated Press writer Jim Salter in Missouri contributed to this report.