WASHINGTON (AP) — The Senate’s top Republican said Monday that GOP candidate Roy Moore should quit his Alabama race amid allegations he had sexual contact with a 14-year-old girl decades ago. Moore fired back that Majority Leader Mitch McConnell is the one who should leave, saying he “has failed conservatives and must be replaced.”

The crossfire escalated a GOP civil war over Moore’s Senate candidacy in a Dec. 12 special election, which until last week was viewed as an inevitable Republican win in the deep-red state. The Washington Post reported that Moore was 32 when he is alleged to have initiated sexual contact with the 14-year-old and pursued romantic relationships with other teenage girls at around that time.

“I believe the women,” McConnell, R-Ky., said Monday in response to a question at an appearance in Louisville. And he said flatly that Moore should step aside for another GOP candidate.

When the Post’s story first broke Thursday, McConnell had said Moore should step aside if the allegations were true.

Shortly after McConnell made his remarks Monday, Moore tweeted his response.

“The person who should step aside is @SenateMajLdr Mitch McConnell. He has failed conservatives and must be replaced. #DrainTheSwamp,” Moore wrote.

McConnell said a write-in effort by another candidate was a possibility.

“That’s an option we’re looking at — whether or not there is someone who can mount a write-in campaign successfully,” McConnell said. Asked specifically about current Sen. Luther Strange, the loser to Moore in a party primary, he said, “We’ll see.”

On the Democratic side, one of the Senate’s moderate members is helping Moore’s challenger raise campaign funds, underscoring the party’s wary approach in an Alabama race that until recently was viewed as a virtually certain win for the GOP.

In fact, the fundraising bid by Sen. Joe Donnelly, D-Ind., doesn’t mention allegations about Moore.

“Doug’s opponent, Roy Moore, is an extremist with a record of putting political ideology above the rule of law,” Donnelly wrote in a weekend email soliciting contributions for Democrat Doug Jones. Moore and Jones face a Dec. 12 special election to replace Strange, who was appointed to replace Jeff Sessions when Sessions was named U.S. attorney general.

Donnelly’s email also cites Jones’ background as “the son of a steelworker” and a prosecutor who “worked to lock away members of the KKK and terrorists for despicable acts of violence.”

Donnelly faces re-election next year in Indiana and is considered one of his party’s most endangered incumbents.

In a further indication of Democrats’ caution, the party’s No. 2 Senate leader, Richard Durbin, dodged a question Sunday about what the Senate should do if Moore is elected. He tried to shift the focus back to Republicans.

“President Trump is the leader of the Republican Party in America. It’s his responsibility to step forward and say more and do more when it comes to the situation in Alabama,” Durbin, D-Ill., said on CNN’s “State of the Union.”

Moore said a lawsuit will be filed over the Post report that detailed the allegations against him.

While pressure to quit the race four weeks before Election Day intensified from within the Republican Party, Moore assured supporters Sunday night at a Huntsville, Alabama, gym that the article was “fake news” and “a desperate attempt to stop my political campaign.”

Moore said allegations that he was involved with a minor child are “untrue” and said the newspaper “will be sued,” drawing a round of applause. The former judge also questioned why such allegations would be leveled for the first time so close to the special election in spite of his decades in public life.

“Why would they come now? Because there are groups that don’t want me in the United States Senate,” he said, naming the Democratic Party and the Republican establishment and accusing them of working together. He added, “We do not plan to let anybody deter us from this race.”

The Post story quoted four women by name, including the woman who alleged the sexual contact at 14, and had two dozen other sources.

Moore, too, has tried to raise money from the controversy, writing in a fundraising pitch that the “vicious and sleazy attacks against me are growing more vicious by the minute.”

Even if Moore were to step aside, his name would likely remain on the ballot. And any effort to add Strange as a write-in candidate would threaten to divide the GOP vote in a way that would give the Democratic candidate a greater chance of winning.

Moore is an outspoken Christian conservative and former state Supreme Court judge.

While he has called the allegations “completely false and misleading,” in an interview with conservative radio host Sean Hannity he did not wholly rule out dating teenage girls when he was in his early 30s. Asked if that would have been usual for him, Moore said, “Not generally, no.”

The situation has stirred concern among anxious GOP officials in Washington in a key race to fill the Senate seat once held by Sessions. Losing the special election to a Democrat would imperil Republicans’ already slim 52-48 majority. But a Moore victory also would pose risks if he were to join the Senate GOP under a cloud of sexual misconduct allegations.