By the end of the 2017 U.S. Senate race in Alabama, Senate Republicans made clear they would rather have a Democrat with them in the Senate than Roy Moore, who was accused by more than half a dozen women of predatory behavior when they were teenagers and he was in his 30s. Senate Republicans got their wish.

But their Roy Moore nightmare is not over. Moore announced Thursday he is running for Senate again, and there is not a lot that Republicans in Washington can do to stop him from running — or even winning.

“Yes, I will run for the United States Senate in 2020,” Moore told reporters in Montgomery, Ala. “Can I win? Yes, I can win.”

Can he, though? More Alabama voters have an unfavorable opinion of Moore than a favorable one, said Brent Buchanan, a national Republican pollster with ties to Alabama. “But he has a vocal group of supporters,” Buchanan said in an email to The Fix.

Moore enters a crowded primary field of four other Republican candidates consisting of a congressman (Bradley Byrne), a former Auburn University football coach (Tommy Tuberville), a state representative (Arnold Mooney), Alabama Secretary of State John Merrill and possibly even Jeff Sessions, who held the seat until he left in 2017 to become attorney general and who Washington Republicans are now floating as a possible candidate again.

Barring a run by Sessions, a field of candidates lesser-known than Moore works in Moore’s favor. Buchanan estimates that Moore could coalesce his dedicated base to get 20 percent of the vote.

From there — well, Moore got that far and nearly won a Senate seat despite Senate Republicans’ actively trying to derail his candidacy. Actually, they’re going to try to do that again.

“We’ll be opposing Roy Moore vigorously,” Senate Majority Leader Mitch McConnell (R-Ky.) told reporters Thursday.

In 2017, Alabama held a special election to replace Sessions. Moore was an outside shot in the primary but ended up winning it. He seemed to be on his way to being the next senator from Alabama until The Washington Post reported the allegations a month before the election.

Moore stayed in the race despite Senate Republicans’ urging him to drop out. One thing he had going for him then was President Trump.

Trump, never one to shy away from defending men accused of behaving badly, was the only public figure in Washington willing to stand by Moore.

But this time, Moore may have to win a primary without the support of the most popular politician in Alabama.

Trump recently tweeted that he did not think Moore could win and that he should stay out of the race.

It is a 180-degree turn from Trump’s position on Moore two years ago. But then again, being the first Republican to lose a Senate seat in Alabama in three decades will change many minds.

Trump’s son Donald Trump Jr. was more direct about what Trump World wants Moore to do this time:

Moore has won in Alabama without Trump before. He won his runoff against Republican interim Sen. Luther Strange in 2017, even though Trump endorsed Strange.

“I’m not going against President Trump at all,” Moore said when asked by reporters Thursday. “I support President Trump. I vote for him. Whether he votes for me or not, I’ll see. I’m sure he will — when I get in the general election.”

The point is, whether Moore wins or loses is in the hands of Alabama voters, not Washington Republicans'.

If Moore wins, that is when the ball gets tossed in Republican leaders’ court. And they have a couple of not-surefire options to try to keep him out of the Senate.

Last time, Senate Republicans were considering kicking him out of the Senate if he won. That would require an overwhelming majority. No sitting senator has been expelled by his peers since the Civil War.

They also considered supporting a write-in candidate, such as maybe Sessions. That idea quickly foundered when Sessions said no, and it was impossible to find another candidate so well known that people could remember how to spell his or her name to write the person in.

Actually, a lot of the Republicans’ Roy Moore problems could be solved by Sessions. It is possible he could run for his old Senate seat now that Trump pushed him out of the attorney general job. His former colleague Sen. Richard C. Shelby (R-Ala.) said Wednesday that Sessions had not dismissed the idea. You can be sure they are lobbying him behind the scenes. Sessions is by far the biggest name of them all, given that he held the seat for 20 years.

But if Sessions does not get in and Moore wins this Senate race, the likeliest scenario is Moore becomes, and remains, the next U.S. senator from Alabama.

The Senate has a long-standing, unwritten rule that it does not expel someone for conduct known to the voters at the time that senator was elected, Cornell Law School professor Josh Chafetz told me in 2017. The thinking behind that is to avoid a slippery slope where the Senate is overriding the will of the voters.

There is a middle ground between kicking Moore out and ignoring his accusers, I wrote in 2017 when ranking the scenarios:

The Senate could vote to censure Moore, which is essentially a public and official reprimand.
That might make it more difficult for Moore to do his job effectively, since other senators won’t want to author legislation with an outcast. But it would allow Moore to keep his job while giving Senate Republicans an opportunity to express their displeasure that Moore is their colleague.

The 2017 U.S. Senate special election in Alabama underscored how unpredictable politics is in the Trump era. It tested the limits of party loyalty over morality in a society newly sensitive to sexual misconduct. If Moore does run, all of that could be litigated again. And there is not much that Washington Republicans can do about it.

This post has been updated.