Last week, Jeff Sessions announced that he’s running for the U.S. Senate in Alabama, the same seat he held for 20 years before resigning to become U.S. Attorney General in 2017. But although Sen. Doug Jones is the most vulnerable Democrat up in 2020, and Sessions has had a long, successful history with the Alabama GOP, he’s far from a shoo-in for 2020.

At first blush, you might expect Sessions to get a warm welcome from Alabama Republicans. After all, he was well-liked in his Senate days — his net approval rating (approval rating minus disapproval rating) in 2016 was nearly 30 points, according to Morning Consult. And he was reelected three times to the chamber, and each time by crushing margins — even going unopposed in 2014 — before he resigned to join Trump’s Cabinet in 2017. So in theory, Sessions could swoop in and become the leading Republican contender by way of his outsized political profile, as there isn’t a clear front-runner yet. There’s just one problem: President Trump.

Trump is still angry at Sessions because when he was his attorney general, Sessions recused himself from the investigation into Russian interference in the 2016 election, leaving Trump without an attorney general to defend him. So Trump’s disdain for Sessions could undermine his bid, as the president remains very popular in Alabama. In fact, Trump had a +22 net approval rating there in September, the president’s highest mark in any state, according to Morning Consult. What’s more, Republican Senate Majority Leader Mitch McConnell has expressed concern about Sessions’s bid. That’s because a chaotic primary could potentially hurt the party’s chances of winning a seat the GOP should be favored to win back in strongly Republican Alabama.

So far, we only have one primary poll to go on that includes Sessions, but it provides some positive news for him, albeit from a friendly source. The Club for Growth, a conservative advocacy group that pushed for Sessions to run, released a survey that found Sessions leading the Republican field with 36 percent of Republican primary voters supporting him, ahead of former Auburn University football coach Tommy Tuberville’s 23 percent, while Rep. Bradley Byrne and former Chief Justice of the Alabama Supreme Court Roy Moore (who lost the 2017 special election to Jones) each had 11 percent. And although he led that poll, Sessions’s support would still be insufficient to avoid a primary runoff, as Alabama is one of seven states that requires a candidate to win a majority of the vote in order to capture the nomination. The runoff system could be a real problem for Sessions, too. While Sessions might garner the most votes in the primary — good enough to win in most states — Trump could end up endorsing his opponent in the runoff, making it tougher for Sessions to attract enough additional support to win a majority.

And other leading Republican candidates don’t appear likely to make way for Sessions’s entrance into the race. Just before Sessions announced, Tuberville said that Sessions “had a chance to help President Trump, and he failed him once.” “We don’t need him to fail him again,” he added. A pro-Tuberville political action committee is also running an ad calling Sessions a “traitor” to Trump. Meanwhile, Byrne said it would be tough for Sessions to win with Trump calling him “an embarrassment to the great state of Alabama.”

No Republican has Trump’s endorsement yet, but it’s pretty clear that Sessions’s opponents are angling for it. In his defense, Sessions is working to combat claims that he’s anti-Trump. In his announcement speech, Sessions said “the president is doing a great job for America and Alabama, and he has my strong support,” highlighting the fact that when Trump ran for president, Sessions was the first senator to back him. It’s clear that Sessions is wise to his greatest weakness (Trump); the big question is whether Alabama Republicans are willing to overlook Trump’s feelings to back him.