It has not been a good week for Senate Republican leaders. A last-ditch effort to repeal the Affordable Care Act didn't even come up for a vote because they couldn't get a majority of Republicans to support it. An establishment GOP senator announced that he's retiring next year. And Republicans in Alabama just nominated former state chief justice Roy Moore to replace Attorney General Jeff Sessions in the U.S. Senate.

Of all those things, Moore's win could be the biggest headache for Senate Republicans. That's because it exacerbates the problems Republicans already face in passing legislation, tamping down insurgent factions and having a good election next year.

1. It's not a guarantee Moore will win the general election

Roy Moore speaks at a campaign rally Monday. (Scott Olson/Getty Images)

Tuesday's runoff between two Republicans was probably the big battle. Alabama hasn't elected a Democrat to the Senate in more than 30 years. (And that Democrat was Sen. Richard C. Shelby, who is now a Republican.)

But Moore is no traditional Republican. He's an unapologetic evangelical conservative who waves handguns at rallies, prides himself on being removed as the state's top judge twice for bringing religion into the job, and as recently as December said he didn't think Barack Obama was a natural-born citizen, and thus qualified to be president. Alabama voters don't mind Christian conservatives, but some political operatives worry that Moore is such a one-issue candidate that he may not be able to reach voters who are worried about other things, such as the economy.

That leaves an opening for the Democratic candidate, Doug Jones, a former U.S. attorney. He'll need lots of outside help to make this a race, because this is still Alabama, which supported President Trump by 26 points in November. But conventional wisdom is that Moore's win in the December general election is not as much of a lock as interim Sen. Luther Strange's would have been.

2. Senate Republicans have probably lost a reliable vote

Sens. John Barrasso (R-Wy,), left, and Senate Majority Leader Mitch McConnell (R-Ky.), head to a news conference in July on Capitol Hill. (Katherine Frey/The Washington Post)

In his couple of months serving as interim senator, Strange usually voted the way Senate leadership wanted Republicans to vote, and a super PAC allied with Senate Majority Leader Mitch McConnell (R-Ky.) spent millions to try to keep Strange in the seat.

Moore, however, beat Strange precisely because he didn't present himself as an establishment figure. And if he gets to Washington, he probably won't forget what got him there. It certainly wasn't McConnell.

Republicans won't be able to count on his vote for much of anything, which is the last thing they need, given that they've twice now fallen one or two votes short of repealing the Affordable Care Act. Other big items on their to-do list, such as tax reform, won't be any easier to pass in a divided party.

Plus, Moore has demonstrated a remarkable lack of understanding of policy. In July, he didn't know what the Deferred Action for Childhood Arrivals program was, despite a radio host explaining it to him.

3. Moore's win could embolden the Bannon wing

Former White House chief strategist Stephen K. Bannon in April. (Carolyn Kaster/Associated Press)

Trump's former chief strategist, Stephen K. Bannon, has already declared war on Republicans in Congress. He backed Moore and he's considering raising money to try to oust GOP senators who have gone against Trump.

Republicans who backed Strange point out that Bannon didn't really hug Moore tight until a couple of weeks before the runoff. But Bannon can declare victory anyway. His guy, not the guy the entire Republican establishment backed, won. Why not try to build on that success in states such as Arizona, against Sen. Jeff Flake; Nevada, against vulnerable Sen. Den Heller; or Mississippi, against Sen. Roger Wicker?

Notice those are all Republicans Bannon would be targeting. Which brings us to our next point.

4. Moore's win could exacerbate a divisive primary season

A challenge from the right in states such as Nevada and Arizona is the opposite of helpful for Senate Republicans. Heller and Flake are pretty much the only two vulnerable Senate Republicans up for reelection in the 2018 midterm election. But first they'll have to beat primary challengers that may be better financed, thanks to an emboldened Bannon.

And the intraparty wars may not be contained to just Nevada and Arizona. “A successful Moore campaign suggests that other primary challengers could succeed, backed by different funding sources than the GOP establishment,” points out Molly Reynolds, a congressional expert at the Brookings Institution.

Control of the Senate isn't really up for grabs in 2018. But a divisive primary season means fewer resources to protect their two vulnerable incumbents and to try to oust 10 Democrats up for reelection in states Trump won.

5. Moore has some highly controversial views

And other Senate Republicans already have begun to answer for them. Here's Sen. Ron Johnson (Wis.) on CNN on Wednesday morning being asked whether he agrees with Moore that Obama is a Muslim, or that God can supersede federal law, or that “homosexual conduct should be illegal.”

It's like Republicans are dealing with a Trump figure all over again.