After the election, though, is a different story. If nearly half of Senate Republicans join with all 48 Democratic senators, they could kick out the newest Alabama senator shortly after he takes a seat. The Constitution lets the Senate censure or even expel its members, but it hasn't successfully happened since the Civil War. In the wake of allegations that Moore dated teenage girls and touched a 14-year-old inappropriately (an allegation he denies), some senators seem to be considering it.
Sen. Cory Gardner (R-Colo.), chair of the committee charged with electing Senate Republicans, said in a statement Monday that if Moore refuses to withdraw from the race and he wins, the Senate "should vote to expel him, because he does not meet the ethical and moral requirements of the United States Senate."
Yes, the Senate can do that. But it's not easy, and it hasn't happened in a long time. Here's how it would work, as guided by Senate procedural experts Sarah Binder of the Brookings Institution and Josh Chafetz of Cornell Law.
1. Decide whether they can stop him from taking the seat: The Senate has constitutional power to decide whether to seat someone the voters elect, and that only requires a majority vote, Chafetz said. But the rules around this are pretty strict and probably don't follow this case: The Senate can only prevent someone from taking their seat if they either weren't duly elected or don't have the constitutional qualifications to be a senator (like being under the age of 30 or not a U.S. citizen). "They can’t just exclude someone because they don’t like him or even because he has committed a crime; it has to be because he’s not actually entitled to a seat," Chafetz said.
2. The Senate's Ethics Committee moves to conduct an investigation into Moore: Just like the Senate is running its own investigation into Russia meddling, senators almost certainly wouldn't vote to expel one of their own based on one news report, no matter how carefully reported it is. (As far as litigating decades-old sexual allegations in the media goes, this story is as close to proof as reporters can get.) They'd launch their own investigation, likely calling in witnesses and perhaps even talking to Moore himself.
One open question is whether his accusers would be willing to testify, either publicly or behind closed doors, potentially putting themselves through more trauma and scrutiny. A fifth Moore accuser who publicly shared her story Monday, Beverly Young Nelson, said she would be willing to testify under oath that Moore sexually assaulted her when she was 16.
3. If the committee finds grounds to expel Moore, Senate Majority Leader Mitch McConnell (R-Ky.) decides to bring up the question of expulsion for a vote before the full Senate. He hasn't commented publicly on whether he's even considering this. But on Monday, he did say he believes Moore's accusers and that Moore should voluntarily leave the race. He also didn't rule out helping sponsor a write-in campaign.
4. Two-thirds of the Senate votes to expel him: That means all 48 senators who caucus with the Democrats, plus 19 Senate Republicans.
This last step in particular is an extraordinarily high bar to clear; getting a two-thirds majority in the Senate is one of the hardest things to do in politics. The requirement in the Senate to expel a senator is the same required to override a veto or change the Constitution. The last time the Senate had this much agreement on a controversial topic was when it sent new Russia sanctions to President Trump's desk.
Though, if an ethics committee did decide that there was grounds to expel Moore, it'd probably become much easier to get behind the idea.
Expelling a senator is also extraordinarily rare. Binder said the last senator expelled by the Senate was in 1862, when the Senate voted to expel more than two dozen members on the grounds of supporting the Confederacy during the Civil War.
A century later, the Senate twice got close to kicking out senators only to see them step down. Moore's defiance to establishment Washington throughout this entire campaign suggests that's not something he'd consider.
There's another roadblock to getting rid of Moore. The Senate has a long-standing, unwritten rule that they don't kick out someone for conduct known to the voters at the time that senator was elected, Chafetz said.
The thinking behind that is to avoid a slippery slope where the Senate is overriding the will of the voters.
For now, this is mostly a theoretical debate. It's possible that Democrat Doug Jones beats Moore in the election next month. Before the allegations, Jones was already within a six-point margin, according to a RealClearPolitics average of polls. Afterward, some polls show him even.
But if Moore does pull out a win, the Senate could seriously consider doing something it hasn't done in more than a century: unseat one of their own.