WASHINGTON — Josh Hawley became the first senator on Wednesday to take up President Trump’s demand that lawmakers challenge the results of the 2020 election, saying he would object to Congress’s certification of the Electoral College results on Jan. 6.
The move by Mr. Hawley, Republican of Missouri, is unlikely to alter the outcome of the election, but it will force Republicans to publicly affirm President-elect Joseph R. Biden Jr.’s victory in a politically fraught test of loyalty to Mr. Trump.
Mr. Hawley, an ambitious freshman senator, framed the objection as “an effort to highlight the failure” of states “to follow their own election laws as well as the unprecedented interference of Big Tech monopolies in the election.” He did not repeat the president’s false claim of widespread voter fraud.
“Millions of voters concerned about election integrity deserve to be heard,” Mr. Hawley said in statement. “I will object on Jan. 6 on their behalf.”
The decision ensures that the certification process, typically a formality, will instead become a debate on the House and Senate floors, elevating Mr. Trump’s repeated false assertions. The Constitution requires that challenges to the certification process be endorsed by lawmakers in both the House and Senate. While Mr. Trump’s most strident allies in the House had announced that they would object to Congress’s effort to certify the Electoral College results, they had so far been unable to persuade a member of the Senate to publicly back their effort.
For most in Mr. Hawley’s party, however, his announcement came as an unwelcome gesture. Republican leaders had hoped to shield their members — especially those up for re-election in 2022 — from such an up-or-down vote, which requires that they publicly endorse or object to the election results.
Senator Mitch McConnell, Republican of Kentucky and the majority leader, had privately urged lawmakers this month to refrain from registering an objection.
But Mr. Hawley hinted on Wednesday that other senators could soon join his effort.
“A number of offices have reached out via staff to ours and said we’re interested,” he told reporters on Capitol Hill. “But does that mean that they will? I don’t know yet.”
“At a time when you would expect the party to be uniting in opposition to the Biden agenda, it is instead increasingly divided over Trump’s 11th-hour actions,” said Alex Conant, a veteran Republican strategist. “There is no political capital to be gained from these fights. This is a very serious person doing a very unserious thing.”
The objection will force the Senate to debate Mr. Hawley’s claim for up to two hours, followed by a vote affirming Mr. Biden’s victory. Rejecting the challenge requires a simple majority vote. For Congress to sustain Mr. Hawley’s opposition, both chambers would have to do so, a virtual impossibility given that Democrats control the House.
Senate Republicans have shown a greater willingness to buck the president’s demands in the final weeks of his presidency, resisting his call to approve $2,000 stimulus checks and preparing to override his veto on the annual military bill.
But the risk of internal political backlash for Republicans who vote to quash the effort is far from theoretical. After Senator John Thune of South Dakota, the No. 2 Republican, said that he hoped senators would realize the election was over and that attempts to overturn the outcome would “go down like a shot dog,” Mr. Trump called on Twitter for Mr. Thune, who is up for re-election in 2022, to face a primary challenge. “Political career over!!!” the president added.
The issue could become particularly charged for two Georgia Republicans, Senators Kelly Loeffler and David Perdue, who are facing tight runoff elections next week that will determine control of the Senate.
“Everything’s on the table right now,” Ms. Loeffler said at a campaign stop at the Ocmulgee River Gun Club in Macon, Ga. “That vote is Jan. 6, and I’m going to continue to fight for this president because he fought for us.”
The parallel effort in the House is being led by Representative Mo Brooks, Republican of Alabama, who has said there was “serious voter fraud and election theft in this election,” even though there is considerable evidence to the contrary. He is eyeing challenges to the election results in five states — Arizona, Pennsylvania, Nevada, Georgia and Wisconsin — where Trump loyalists claim that varying degrees of fraud or illegal voting took place, despite certification by the voting authorities and no evidence of widespread impropriety.
Those challenges are required to have a senator’s signature affixed, according to the Constitution and the Electoral Count Act of 1887.
The president’s allies and observers on Capitol Hill, aware of the requirement, had openly conjectured whether a Republican senator might join the crusade. When Senator-elect Tommy Tuberville, a former football coach at Auburn University in Alabama, left the door open to lodging an objection in an interview with a local newspaper, Mr. Trump took to Twitter to lavish praise on him, calling him “a great champion and man of courage.”
“More Republican Senators should follow his lead,” Mr. Trump wrote.
But it was Mr. Hawley, not Mr. Tuberville, who ultimately first threw his hat into the ring, a distinction that Mr. Trump or his legions of supporters are likely to notice.
Mr. Hawley, who swept into Washington in 2019 after defeating the incumbent Democrat, Claire McCaskill, has embraced Mr. Trump’s brand of populism in his short time in the Senate, pushing for $2,000 pandemic relief checks and railing against social media companies. He is widely considered a potential contender for the 2024 presidential election.
“This is how you run for president on the Republican side in 2024,” said Senator Amy Klobuchar of Minnesota, the top Democrat on the committee that oversees the certification process. “You join a coup attempt. Democracy will prevail.”
At a news briefing on Wednesday, the incoming White House press secretary, Jennifer Psaki, said that “the American people spoke resoundingly in this election,” and she described Congress’s certification of the Electoral College results as “merely a formality.”
“Regardless of whatever antics anyone is up to on Jan. 6, President-elect Biden will be sworn in on the 20th,” Ms. Psaki said.
Mr. Hawley’s challenge is not unprecedented, even in the modern era. Democrats in both the House and Senate challenged certification of the 2004 election results and House Democrats tried on their own to challenge the 2016 and 2000 outcomes, though without Senate support.
But in none of those cases did they have backing from most party leaders or their defeated presidential nominee.
The last time a senator joined such a challenge was January 2005, when Senator Barbara Boxer of California, along with Representative Stephanie Tubbs Jones, Democrat of Ohio, briefly delayed the certification of George W. Bush’s victory.
In challenging those results Democrats cited claims that Ohio election officials had improperly purged voter rolls and otherwise disenfranchised hundreds of thousands of voters in the state, which Mr. Bush carried by fewer than 120,000 votes. Nancy Pelosi, then the House Democratic leader, supported the challenge. But she and the other Democrats conceded that they did not actually consider the Democratic candidate, John Kerry, to be the state’s rightful winner, and that they were only spotlighting voting rights abuses. The House voted 267 to 31 against the challenge and the Senate rejected it 74 to 1. Mr. Kerry, who was visiting the Middle East at the time, did not support the effort.
After the 2016 election, several House Democrats tried again, rising during the joint session to register challenges against Mr. Trump’s victory over Hillary Clinton in various states. The Democrats cited reasons ranging from long lines at polling sites to the Kremlin’s election influence operation.
But no senators supported them, leading the departing vice president presiding over the session — Mr. Biden — to gavel down the House members’ verbal objections and declare, “It is over.”
Thomas Kaplan contributed reporting from Washington, and Astead W. Herndon from Macon, Ga.
