Here's a rundown of this fascinating Republican vs. Republican battle Tuesday, which could reverberate far beyond Alabama.
Sen. Luther Strange: a.k.a “Big Luther” (he's 6-foot-9). He's holding the Senate seat after being appointed in February. But one huge problem for Strange: The governor who appointed him to the seat resigned soon after and pleaded guilty to misdemeanors related to allegations of an affair and use of public resources to carry it out and cover it up.
Strange came in second in a crowded primary on Aug. 15 to …
Roy Moore: a former Alabama chief justice and a well-known culture warrior. Moore was kicked off the bench in September after an ethics commission said he tried to block same-sex marriage in the state.
He was also suspended in the 1990s as a circuit judge when he hung a wooden plaque of the Ten Commandments behind his bench and refused to take it down.
CNN found that just last year, Moore said he didn't think Barack Obama was a natural-born citizen, and thus qualified to be president. And the Washington Examiner uncovered that this summer that Moore didn't know what the Deferred Action for Childhood Arrivals program was.
The state of the race …
… is not good for Strange. In the Aug. 15 primary, Moore received 39 percent of the vote, while Strange got 33. Polling since then shows Moore with an edge over Strange.
That's despite the fact that Trump, who is liked by more than 80 percent of Alabama voters even as polling on Strange goes down, endorsed Strange and held a rally for him Friday (although he wavered on his support, wondering out loud on stage if he had made a mistake).
Strange also has the entire Republican establishment behind him: Senate Majority Leader Mitch McConnell's allied super PAC has spent more than $2.5 million for him, and the National Rifle Association and Senate Republicans' campaign arm support him.
Moore has none of that, save a nod from Trump's former chief strategist Stephen K. Bannon and Ben Carson, the Housing and Urban Development secretary.
In this anti-establishment climate, less can be more. It's not unlike how a man who had never held public office before beat 16 well-qualified politicians for the GOP presidential nomination.
On paper, Strange, a former Alabama attorney general, is a solid candidate. But he has struggled to translate that to voters. That's another parallel to the 2016 race, where candidates such as Jeb Bush, Marco Rubio and Scott Walker struggled to gain traction despite their long résumés.
“Roy Moore is a political phenomenon like Donald Trump,” said Brent Buchanan, a Montgomery-based GOP consultant. “Strange is struggling to gain traction against the insurgent-like approach of Moore and his fervent supporters.”
If Strange loses, Trump and Senate Republicans might need a gut check
Tuesday is just one election that Republicans up for reelection will be watching closely.
A Strange win would bring “a sigh of relief [to the GOP establishment] without question,” said Brett Cowden, a GOP strategist with Cygnal.
A Moore win could demonstrate the limits of Trump's power in conservative circles and potentially mark him as — gasp — the establishment. Or not.
“Prior to the rally in Huntsville this weekend, Trump’s support consisted almost entirely of a few tweets,” Cowden wrote to The Fix in an email. “The president’s supporters like Trump and they like Moore. They don’t think they have to choose.”
Even if a Moore win doesn't change Trump's standing with voters, it could change the calculations of Senate Republicans either facing reelection or deciding whether to run for reelection. Senators in states such as Arizona, Mississippi, Nevada and Tennessee could either decide to call it quits or up their resources by a factor of 10 just to be on the safe side of a primary challenge.
“If you are a GOP senator who’s on the fence about running again and you see Moore beat Strange (even when Strange had the backing of McConnell and his money), that could affect your decision,” said Molly Reynolds, a congressional expert at the Brookings Institution. " She added that “the resources the GOP has to spend propping up incumbents in primaries are resources they don’t have in the fall” to try to topple vulnerable Democrats.