Senate Democrats are in a tough spot over Sen. Kyrsten Sinema’s (I-Ariz.) surprise announcement that she will leave the Democratic Party: looking to keep her close in the tightly divided chamber even as some in the party look to oust her in 2024. Sinema’s decision to register as an Independent creates the prospect of a three-way general election race for her seat, which Republicans believe would give them a clear path to picking it up. Arizona Democrats are already talking about potential challengers, including Rep. Ruben Gallego (D-Ariz.) and Rep. Greg Stanton (D-Ariz.), showing no sign that they’ll give Sinema...