WASHINGTON — Senate Republican leaders on Monday waged an urgent campaign to pressure nominee Roy Moore to withdraw from the Alabama Senate race amid allegations of sexual misconduct, declaring him “unfit to serve” and threatening to expel him from Congress if elected.

But Moore showed no signs he was preparing to step aside, even as another woman came forward to accuse him of sexually assaulting her in the late 1970s when she was 16 years old.

The fusillade from Senate Republicans started Monday morning in Louisville, where Majority Leader Mitch McConnell, R-Ky., called on Moore to step aside.

“I believe the women, yes,” he said of the allegations leveled against Moore.

Later, National Republican Senatorial Committee Chairman Cory Gardner, R-Colo., issued a written statement going even further. “If he refuses to withdraw and wins, the Senate should vote to expel him,” Gardner said. He later told reporters Moore “doesn’t belong in the United States Senate.”

The public comments from top Republican senators marked a dramatic escalation from their initial reactions to Thursday’s Washington Post report detailing allegations that Moore initiated a sexual encounter with a 14-year-old girl when he was 32.

The intensifying move against Moore reflected a growing sense that his candidacy is becoming a national emergency for the Republican Party, which is already deeply concerned about its standing with voters ahead of the 2018 midterm elections. In campaigns far from Alabama, Democrats on Monday sought to tie Republican candidates to Moore to take advantage of the controversy surrounding the former judge.

Still, national Republican leaders and their allies were left without a clear path forward, with no way to remove Moore’s name from the ballot for the Dec. 12 election. One possibility that some Republican officials were pushing as a last-ditch effort was a write-in campaign by Attorney General Jeff Sessions, who vacated the seat to join the Trump administration.

But there was considerable skepticism in Sessions’ orbit that he would agree to that idea. Others floated the prospect of a write-in effort for Sen. Luther Strange, R-Ala., whom Moore defeated in the primary.

Sen. Richard Shelby, R-Ala., was among the Republicans voicing confidence that Sessions would be the party’s best hope as write-in candidate. He told reporters the attorney general would be a “strong one.”

President Trump has been relatively quiet on the controversy in recent days while traveling in Asia, adding a degree of uncertainty to how the party should proceed with Moore. Last week, White House press secretary Sarah Huckabee Sanders said Trump believed that if the allegations against Moore are true, he “will do the right thing and step aside.”

In recent days, senior Trump administration officials have been in touch with Alabama Gov. Kay Ivey, R, and her inner circle, according to several people briefed on the talks. One person described those conversations as “information gathering” so the White House would know where Ivey stands and to keep the channels of communication open as the political drama continues.

But since Trump won’t return from Asia until late Tuesday and is still considering his own options regarding how to further address Moore’s candidacy, White House officials have been reluctant to lean on Ivey in any way, the people said.

“It’s tough having him out of town because no one wants to get too far ahead of him,” said one Republican involved in the talks, requesting anonymity to describe private deliberations.

McConnell has spoken to Trump about Moore since the allegations were first reported last week, a Republican familiar with their conversations said. Senate Republican leaders and their allies believe that Trump’s positioning – wherever he decides to come down – will be crucial to the attempt to force Moore out.

Gardner’s call to expel Moore if elected was Senate Republican leaders most aggressive effort yet to get the former judge to drop out of the race. But an effort to expel a senator is extremely rare and would require the approval of two-thirds of the chamber to be successful. An actual vote hasn’t happened since 1862.

Moore was defiant amid the increasing pressure from party leaders. He wrote on social media that McConnell is the one “who should step aside” and that he has “failed conservatives.”

The war of words unfolded on the same day that Beverly Young Nelson, now 55 , accused Moore, now 70, of sexually assaulting her and bruising her neck in the late 1970s when she was 16 years old.

Nelson said at a news conference at a New York hotel that Moore, then the district attorney of Etowah County, was a regular at a restaurant, the Old Hickory House restaurant in the northeastern Alabama town of Gadsden, where she was a waitress and would sometimes compliment her looks or touch her long red hair. She showed a copy of her high school yearbook that she said Moore signed on Dec. 22, 1977, with the inscription: “To a sweeter more beautiful girl I could not say ‘Merry Christmas.’ ”

On a cold night about a week or two after that, Nelson alleges that Moore offered to give her a ride home from work after her shift ended at 10 p.m. Instead of taking her home, Nelson said that Moore pulled the two-door car into a dark and deserted area between a dumpster and the back of the restaurant.

When she asked what he was doing, Nelson alleges that Moore put his hands on her breasts and began groping her. When she tried to open the car door and leave, Nelson said he reached over and locked the door. When she yelled at him to stop and tried to fight him off, she alleges that he tightly squeezed the back of her neck and tried to force her head toward his lap. He also tried to pull her shirt off, she said.

Moore denied this latest accusations during a brief campaign appearance Monday evening in Etowah County, where he still lives.

“I can tell you without hesitation this is absolutely false,” Moore said, according to the Anniston Star newspaper. “I never did what she said I did. I don’t even know the woman. I don’t know anything about her. I don’t even know where the restaurant is or was.”

The new allegation followed an extensive report published Thursday by The Washington Post in which Leigh Corfman alleged that Moore initiated a sexual encounter with her when she was 14 and Moore was a 32-year-old assistant district attorney. Moore has denied the accusation.

In addition to Corfman, three other women interviewed by The Post in recent weeks said Moore pursued them when they were between the ages of 16 and 18 and he was in his early 30s, episodes they said they found flattering at the time, but troubling as they got older. None of the three women said that Moore forced them into any sort of relationship or sexual contact.

Neither Corfman nor any of the other women sought out The Post. While reporting a story in Alabama about supporters of Moore’s Senate campaign, a Post reporter heard that Moore allegedly had sought relationships with teenage girls. Over the following three weeks, two Post reporters contacted and interviewed the four women.