Voters in Alabama who pick up the phone on Tuesday might hear the voice of President Donald Trump, his predecessor Barack Obama or former vice president Joe Biden advocating for one of the candidates in the state's Senate special election.

But they won't hear from the current vice president, Mike Pence, who in a rare break with his boss has gone silent on a race that could narrow Republican control of the Senate. The election pits Republican Roy Moore, who has been accused by several women of sexual misconduct while they were teenagers, against Democrat Doug Jones.

Pence hasn't commented publicly about the race since Nov. 9, when a spokeswoman called the allegations against Moore "disturbing." His absence stands out after Trump and the Republican National Committee reversed their abandonment of Moore and moved last week to fully support him despite the allegations. In contrast with his thrice-married boss, who's faced his own allegations of misconduct with women, Pence is an evangelical conservative whose political career is marked by strong stands on moral issues such as abortion.

"With the most controversial candidate running for the Senate in recent memory, you have the president getting engaged and you have the vice president really sort of disappearing," said Joel Goldstein, who teaches law at St. Louis University and has written books on the vice presidency. "This could be a political judgment that silence is the best course."

Spokesmen for Pence and Trump did not respond to requests for comment.

Some Republicans who regard Moore's candidacy as an existential threat to the party say that the vice president is wrong to sit out the race.

"Pence's silence is being complicit," said Rick Tyler, a GOP strategist and former spokesman for Sen. Ted Cruz's presidential campaign. "He's trying to sit it out. I don't know where he stands. He's not providing any leadership."

In November, the Washington Post published the accounts of four women who said Moore pursued them for dates and sexual encounters decades ago when they were teenagers and Moore was in his 30s. One of them was 14 at the time. Another woman has accused Moore of sexually assaulting her when she was 16. Moore has denied the accusations and his campaign has attacked the credibility of the women speaking out against him.

The allegations have turned the race in Republican-dominated Alabama into a competitive contest, with top Democrats like Obama and Biden recording robo-calls to gin up support for Jones. Trump has recorded a robo-call for Moore.

Before the Post story, Pence offered his full endorsement of Moore. Like his boss, the vice president had initially backed Moore's primary opponent, Sen. Luther Strange.

"Congratulations Roy Moore! We are thrilled you ran on the #MAGA agenda & we are for you!" Pence tweeted on Sept. 26, just 15 minutes after Trump posted his own congratulatory message after Moore defeated Strange.

But after the Post report, which included several on-the-record allegations against Moore, Pence's public support evaporated. Pence told The Hill newspaper in 2002 that he doesn't dine alone with women or attend events at which alcohol is served without his wife, Karen -- a standard for his own personal behavior now known popularly as "the Pence rule" after the Washington Post resurfaced it in a story about Karen Pence this year.

In the Nov. 9 statement following the Post's report on Moore, Pence spokeswoman Alyssa Farah said: "The vice president found the allegations in the story disturbing and believes, if true, this would disqualify anyone from serving in office."

That would be Pence's last public comment on the race. Trump initially expressed his own concern about the allegations, but even after he began to signal his support for Moore, his vice president stayed mum.

It is a departure for Pence, who opened his own political action committee earlier this year and has eagerly jumped into other races.

He has regularly amplified Trump's endorsements, often re-posting the president's tweets about candidates or serving as a stand-in on the campaign trail. He has dished out more than $200,000 from his PAC to congressional Republicans.

Pence has also campaigned in a handful of special and off-year elections, lending his personal support to Republican candidates in Virginia, Montana, Georgia, Kansas and elsewhere.

"Don't let Nancy Pelosi and the liberal Democrats take this seat out of Republican hands," Pence said in a recorded call to Montana voters on behalf of Republican congressional candidate Greg Gianforte in May. "The stakes are high, and your vote will matter this Thursday."

Elected Republicans have struggled with the allegations against Moore, which come amid a national furor over powerful men accused of sexually harassing or abusing women. Trump faced his own allegations of misconduct before his election in 2016 after the Post published a recording of Trump boasting of grabbing women's genitals to a television show host.

Pence briefly distanced himself from Trump after the "Access Hollywood" tape was released. He may be taking a similar approach to Moore, Goldstein said.

According to three people familiar with his actions, Breitbart News chairman Steve Bannon made calls to Trump and to Nick Ayers, Pence's chief of staff, urging them to withhold public comment and let the people of Alabama decide whether Moore belonged in the Senate.

Moore enjoys little support among establishment Republicans outside of the Oval Office. The Senate Majority Leader, Mitch McConnell, has said Moore will be investigated by the Ethics Committee if he wins the election.

"The state of Alabama deserves better," the state's senior senator, Republican Richard Shelby, said Sunday on CNN's "State of the Union."