Mr. Shelby, who has said he would write in an unnamed Republican rather than vote for Mr. Moore, is one of the few elected G.O.P. officials in the state to openly abandon their party’s embattled Senate nominee.
Mr. Jones was less voluble when it came to another last-minute turnout tactic: an automated phone call that former President Barack Obama recorded for his campaign. Mr. Jones’s advisers are deciding today whether to deploy the message to help mobilize Democrats. Mr. Jones appeared unenthusiastic about highlighting the involvement of an out-of-state figure who is locally polarizing.
“I know that there have been a lot of robocalls that have been recorded — I don’t know what’s being used,” Mr. Jones insisted.
The tight race is all the more extraordinary by the standards of Alabama, where no Democrat has won an election for Senate or governor in almost 20 years. A Fox News poll published on Monday found Mr. Jones with a 10-point lead over Mr. Moore, but other recent polling has found Mr. Moore ahead, and private Democratic polling shows a closer race.
Still, Republicans and Democrats agree on the basic dynamics of the campaign: If Mr. Jones can turn out young people and African Americans, and peel away a chunk of Republican-leaning whites — particularly women — who recoil from Mr. Moore, then he has a chance to win. Otherwise, the state’s conservative D.N.A. is likely to kick in and rescue Mr. Moore from tribulations of his own making.
The Republican candidate has not held a campaign event in a week, and has only infrequently appeared in public since a series of women came forward to allege that he had pursued them sexually while they were young teenagers.
Mr. Moore is scheduled to emerge from his relative seclusion on Monday evening, with a rally in Midland City, a town of a few thousand people in the state’s rural southeastern corner. If Mr. Jones manages to run up a significant lead in the state’s urban and suburban areas, Mr. Moore will be counting on stronger turnout from his largely evangelical base in smaller communities.
Mr. Moore’s rally appears aimed at driving those voters to the polls. He is scheduled to appear alongside Stephen K. Bannon, the former aide to President Trump, and Representative Louie Gohmert of Texas. Both are well known to activists, largely through their prominence in conservative media, though neither has close ties to Alabama.
Should Mr. Moore prevail on Tuesday, it will probably be the backing of a different out-of-state supporter — Mr. Trump himself — that was most influential in the last days of the race. While Mr. Trump has not visited Alabama, he has tweeted repeatedly in support of Mr. Moore and recorded an automated phone message that was going out to Republican voters.
Mr. Trump provided Mr. Moore with a crucial seal of approval among conservatives at a moment of crisis for his campaign, effectively offering reassurance to Republicans who were uneasy about Mr. Moore’s scandals that it was acceptable to vote for him. At a rally last Friday just over the border in Florida, Mr. Trump hailed Mr. Moore as critical to enacting a “ ‘Make America Great Again’ agenda” in the Senate.
But Mr. Moore, for his part, has plainly struggled to deliver such a pointed closing message, and the most visible public remarks from Mr. Moore and his campaign have been focused in the main on denying allegations of sexual misconduct.
The charges against Mr. Moore broke into the headlines again on Monday morning, when one of the women whom he is said to have dated as a teenager, Debbie Wesson Gibson, rebuked him in an interview with NBC News. “He is unfit for public service, at the Senate level, in this nation,” Ms. Wesson Gibson said of Mr. Moore, describing him as a “creeper.”
Mr. Moore has continued to maintain that he did not date teenagers when he was in his 30s, and has denied sexually abusing a 14-year-old girl.
On Monday morning, Mr. Jones ridiculed Mr. Moore for effectively going underground at the most intense moment in the race. He mockingly alluded to reports that Mr. Moore attended the Army-Navy football game in Philadelphia.
“Here I am once again, surrounded by this gaggle, which I’ve come to love and enjoy, while Roy Moore was not even in the state of Alabama over this weekend,” Mr. Jones said, adding: “When is the last time you’ve heard of a candidate for statewide office leave the state?”