WASHINGTON - Several Republicans have their party’s candidate for a vacant US Senate seat to quit the race if an explosive report that he had a sexual encounter with a 14-year-old girl is true. President Donald Trump cautioned that Roy Moore, a former judge from Alabama, was only facing allegations.

But Trump believes that Moore “will do the right thing and step aside” if the allegations are true, the White House press secretary said aboard Air Force One, before the president landed in Vietnam for a summit.

Four women, speaking on the record, told The Washington Post that Moore pursued them when they were 18 or younger and he was in his early thirties working as an assistant district attorney.

Moore, 70, denied any sexual impropriety. He said on Twitter that he was under attack from the “Obama-Clinton Machine’s liberal media lapdogs” and added that “Christian Conservatives like you and me” must fight against what he called forces of evil. “I will NEVER GIVE UP the fight!”

In an email to his supporters, Moore’s campaign called the Post story “fake news” and said the allegations “would have been made public long before now” if they were true.

Moore, an anti-establishment conservative, faces Democrat Doug Jones in a special Senate election December 12 to replace Jeff Sessions, who is now US attorney general.

The accusations by the four women reverberated through Washington.

“If these allegations are true, he must step aside,” Senate Majority Leader Mitch McConnell said. At least a dozen other Republicans followed suit.

Senator John McCain, the 2008 Republican presidential nominee, immediately declared the allegations “disqualifying” for Moore and called on him to immediately step aside. But in Alabama, state auditor Jim Zeigler brushed off the allegations.

He told the Washington Examiner “there is nothing to see here” - and referred to the Bible as a defense.

“Take Joseph and Mary. Mary was a teenager and Joseph was an adult carpenter. They became parents of Jesus,” Zeigler told the conservative news outlet. “There’s just nothing immoral or illegal here.”

Experts have told US media that Alabama’s Republican Party or Moore himself could withdraw his name from consideration.