Why Arizona Could Be the Most Interesting and Consequential Senate Race of 2024

A rizona Democratic senator Kyrsten Sinema’s announcement that she’s leaving the Democratic Party and registering as an independent sent shockwaves through Washington on Friday.

But it doesn’t appear that Sinema’s move will have much of an impact on the operations of the Senate. She has said she will not caucus with the Republicans and has not yet said whether she will continue to formally caucus with Democrats (as “independent” senators Angus King of Maine and Bernie Sanders of Vermont do).

So the worst-case scenario for Democrats is that they have formal control of the Senate by a 50–49 margin rather than a 51–49 margin. And it doesn’t appear likely to have any practical impact on floor votes over the next two years: Sinema says her new registration won’t affect how she votes on nominees and legislation, and Majority Leader Chuck Schumer says she will keep her committee assignments.

But the Sinema news could shake up what was already shaping up to be the most interesting and consequential Senate race of 2024. That title belongs to Arizona because a Democratic purge of Sinema and victory in the general election are essential for Democrats hoping to nuke the legislative filibuster in 2025.

Nuking the legislative filibuster is a necessary first step for Democrats hoping to pass sweeping federal legislation on abortion, voting, immigration, statehood for the District of Columbia — thereby handing themselves two extra Senate seats — and more.

After the 2022 midterms, there are now 49 Democratic senators who would vote to overcome the 60-vote rule. In 2024, the Democrats’ only opportunities to pick up Senate seats are in Florida and Texas. Considering the results of the 2020 and 2022 elections, “opportunity” is probably too generous a word for the party’s outlook in either of those states, barring some shocking turn of events. That’s why Arizona is key: It’s the only way Democrats could get the 50th vote needed to nuke the filibuster (if they hold the White House and pick up the five seats needed to retake the House).

Republicans, of course, have a few good opportunities to pick up Senate seats in 2024. Their best opportunity is West Virginia. Democratic presidential candidates lost the state by nearly 40 points in 2016 and 2020, and incumbent Democrat Joe Manchin won reelection in the blue wave of 2018 by only three points. But when it comes to protecting or nuking the filibuster, the outcome in West Virginia doesn’t matter, because Manchin is a strong supporter of the 60-vote rule.

The GOP’s two other best chances for Senate pickups in 2024 are Ohio and Montana. Democrats have lost the presidential election in those states by wide margins in recent years, but incumbent Democrats Sherrod Brown and Jon Tester would be formidable.

Sinema has not yet announced whether she will seek reelection in 2024, but if she does it would likely mean a wild three-way race. Republicans would certainly want to win the race outright if they can — control of the Senate would allow them to confirm Supreme Court justices, and Sinema is still a liberal on most issues, including taxpayer funding of abortion. But you could easily imagine a scenario in which Republicans nominate another weak candidate, prompting a critical faction of GOP voters to migrate toward Sinema, either because of distaste for the GOP nominee or a strategic bet that Sinema has the best chance of keeping the seat from a party-line Democrat and preventing the worst-case scenario.