After being fairly timid amid the president’s attacks on him throughout his tenure as attorney general, Jeff Sessions is challenging President Trump in a bold way on his path back to power. And it’s not clear which giant of Republican politics is going to win.

Trump’s former attorney general is expected to announce Thursday that he is running for Senate in Alabama. He will be trying to close the chapter of his career that involved Trump and get back to serving Alabama in the Senate, which he had done for 20 years prior.

Except Sessions must go straight through Trump. Trump is popular in Alabama and doesn’t want Sessions to run, my colleagues have reported. Sessions has also been popular, winning sometimes with as much as 97 percent of the vote when he has run unopposed. It will be a showdown of two political giants in Alabama.

This is not one we expect Trump to back down on. It’s probably fair to say that Trump, before facing impeachment, thought of his former attorney general as the biggest threat to his presidency for recusing himself from the investigation of Russian interference in the 2016 presidential election.

That wasn’t really fair to Sessions, but for our purposes, the truth matters less than Trump’s perception of what happened: Trump hates disloyalty and views his former attorney general as the ultimate disloyal figure, abandoning his presidency at a perilous moment. So Trump attacked him in a fairly mercilessly way before finally firing him a year ago.

But now, Sessions really could be the biggest threat to Trump’s stature among Republicans — right as Trump needs his base to protect him from impeachment. Sessions enters a crowded primary field that includes a candidate Trump has endorsed in the past, Roy Moore, and others he has been told will win, such as Rep. Bradley Byrne (R-Ala.).

Sessions is the biggest name to get into the race, and some in Washington had hoped his entrance would clear the decks to ensure that Moore would not win the GOP primary again. Moore lost the election for Republicans two years ago after being accused of sexual misconduct with teenage girls when he was in his 30s.

But Byrne — much less an obstinate Moore, who got in this time without Trump’s blessing — and some others have not shown any sign they will get out for Sessions. “Alabama deserves a Senator who will stand with the president and won’t run away and hide from the fight,” Byrne said in a statement, taking a shot at Sessions.

So now the race could divide Alabama Republicans even more, and Trump alone probably has the authority to help guide the primary the right way. Unless Republican voters don’t listen to him and choose Sessions over the president’s wishes.

That would be the third embarrassment for Trump in Alabama in two years. In the 2017 special election primary to replace Sessions, Trump backed Luther Strange. Republican voters picked Moore. Trump stayed with Moore for the general election, and Alabama voters elected Democrat Doug Jones. If Sessions wins this primary, it raises the question: How much political capital does Trump have in Alabama, one of the most pro-Trump states in the nation?

But there is more at stake than just political reputations. Republicans would like to win back this seat in Alabama to maintain their control of the Senate majority in 2020. Republicans can afford to lose only three seats if Trump loses the presidency, and they are playing defense in 23 this year. Winning Alabama back gives them some cushion in case Sens. Cory Gardner in Colorado or Martha McSally in Arizona or Thom Tillis in North Carolina or Susan Collins in Maine lose their races.

What happens if Trump can’t unite Republican primary voters in Alabama around a candidate and then a problematic one like Moore, with a dedicated base, rises out of the chaos again? Could Republicans lose Alabama twice? And would Trump be blamed for it?

And then there’s the question of how, if Sessions wins, he might be a thorn in the side of the president should both men find themselves in office after 2020.

While he was attorney general, Sessions rejected Trump allies’ requests to appoint a second special counsel to investigate Democrats’ role in an infamous dossier on Trump’s ties to Russia. But also while Sessions was attorney general, he needed to please Trump to keep his job. If he wins a Senate seat next year despite Trump, he won’t be beholden to the president anymore. And that could have a powerful wave effect on the rest of the Republican Senate caucus.

But we’re getting a bit ahead of ourselves. The first step in this battle for Republican titans happens March 3, when Alabama Republican voters, in effect, will have to choose between Sessions and Trump.