Arizona Sen. Jeff Flake, an ardent critic of President Trump, announced Tuesday that he will not run for re-election in 2018. Flake, a Republican, was arguably the most vulnerable senator of either party who was up for re-election next year because he was almost certain to face strong challenges from both the right (in the GOP primary) and the left (in the general election).

So how does Flake’s exit change Arizona’s 2018 Senate election?

Big picture: It doesn’t. Arizona is likely to remain the Democrats’ best opportunity to pick up a Republican-held seat. But Flake’s retirement could make that pickup more or less likely — we just don’t know which yet.

The general election between the likely Democratic nominee, U.S. Rep. Kyrsten Sinema, and whomever the Republicans nominate starts as a tossup. At this time, the only notable Republican running against Sinema is Kelli Ward, a former Arizona state senator who has closely aligned herself with Trump. Sinema led Ward in an August HighGround Public Affairs survey 32 percent to 31 percent, with 38 percent of voters undecided. Private polling also had Sinema ahead by a small margin. For comparison, polls had Sinema ahead of Flake by high single digits.

So Republicans are lucky Flake stepped down, right? Not so fast.

For one, there’s a good chance that Flake would have lost to Ward in the Republican primary had he remained in the race; polls showed her with a healthy and growing lead.

The general election polls look close, but more than a third of voters are undecided, and Sinema may build a larger lead over Ward as the candidates become better known. Sinema has the most moderate voting record of any Democrat in the U.S. House. Ward describes herself as “very conservative” and is known for making extreme remarks. For instance, shortly after Arizona Sen. John McCain revealed that he had brain cancer, Ward announced that he should resign and that she should be considered for his replacement. (McCain beat Ward in a 2016 primary.) And although Arizona historically votes Republican in general elections, it has been trending more purplish. Trump carried the state by only 3.5 percentage points over Hillary Clinton.

If the GOP nomination now defaults to Ward, Flake’s retirement could end up making a Sinema victory more likely.

But it’s not yet clear that the nomination will default to Ward. Other, more establishment-friendly Republicans may jump into the race now that Flake is out. If one of these non-Ward candidates wins the primary, it probably means that Republicans caught a break with Flake retiring. He was very unpopular with Republicans, after all. And a new Republican candidate may be able to hold the Trump base (which Flake was struggling to do) without alienating voters in the center (as Ward may).

Other potential Republican candidates whose names had been buzzed about — Robert Graham and Jeff DeWit — are on good terms with Trump and are more conventional politicians than Ward. DeWit is the state treasurer, and Graham ran the Arizona Republican Party and got favorable reviews for his efforts to unite the emergent tea party forces with more establishment Republicans. Neither man is a polarizing figure in the state the way Ward is, and as Graham told FiveThirtyEight in September, GOP donors in Arizona have been clamoring for either of them to enter the race and unite establishment Republicans and far-right activists behind a single candidate. Dustin Stockton, Ward’s former campaign manager, told FiveThirtyEight that Rep. Martha McSally is also being talked about as a potential entrant to the race. DeWit seemed to acknowledge the pressure to join the race in a Tuesday-afternoon tweet posted after Flake’s announcement.

Ward, though, has the advantage of having been endorsed by a number of prominent national Republican figures, like Sean Hannity, Laura Ingraham and, most recently, Trump’s former chief strategist Steve Bannon. While she seems like the pick of Trump/Bannon world, there have also been signs that some in that milieu might still be looking for other options. When the president flew to Phoenix for a rally, Trump met with both Graham and DeWit, but Ward was not invited to president’s VIP section. Last week, Stockton and another former Ward staffer — both of whom are also former Breitbart employees — released a statement bashing her.

Either way, it won’t be easy for Republicans to hold the Arizona Senate seat. More Arizonans dislike Trump than like him, and midterm elections are almost always tough on the president’s party. Sinema, meanwhile, is probably the strongest candidate Democrats could have hoped for.