Kyrsten Sinema has been a thorn in the side of Democrats for the last two years. Unlike, co-thorn Joe Manchin, there’s no obvious reason why she insisted on being one. (As Eric Levitz notes, Mark Kelly’s victory is an indictment of Sinema’s politics.) Manchin is from the most pro-Trump state in the country. Sinema’s not.

In recent weeks, Rep. Ruben Gallego has been signaling more and more clearly that he may challenge Sinema in a primary in advance of her reelection campaign in 2024. Normally in such circumstances partisans try to find a balance between disciplining or displacing an errant elected official and the risk of losing the seat altogether. But that mistakes the challenge Democrats actually face. Because Sinema is already unelectable.

Let’s start with the fact that 2024 is going to be a very challenging year for the Democrats to hold the Senate. The pick-up opportunities are challenging at best. Democrats must defend seats in Ohio, Montana and West Virginia. In other words, Democrats can’t afford to lose a seat in Arizona if they have hopes of retaining Senate control.