Sen. Jeff Flake has vocally criticized his party’s freshly elected president, raised little money, and backed a moderate approach to an immigration overhaul.

In other words, the first-term senator from Arizona has all but begged a Donald Trump-like Republican to run against him. Now, his friends and allies fear that’s exactly what will happen — with no guarantee that the incumbent lawmaker will win.

To many GOP officials, no Republican senator is more vulnerable in a primary next year than Flake. The 54-year-old, according to one strategist who reviewed polling data last month, is less popular among likely GOP primary voters in Arizona than even John McCain, who for years has had a famously rocky relationship with his party’s base. The poll showed almost as many primary voters disliked Flake as liked him.

And although he has already drawn a challenger — former state Sen. Kelli Ward, who ran unsuccessfully against McCain last year — his supporters are more worried about another foe, state Treasurer Jeff DeWit.

DeWit was a strong Trump supporter, serving as chairman of his Arizona campaign before becoming his national campaign’s chief operating officer. And people close to Flake worry that DeWit could potentially exploit the senator’s adversarial history with Trump. Flake routinely criticized Trump’s conduct during the campaign, culminating in a tense showdown on Capitol Hill in July.