Throughout much of 2021, left-of-center political analysts often asked themselves, What is Kyrsten Sinema’s deal? As she battled all year against simple Senate passage of the Build Back Better legislation, and against the filibuster reforms needed to enact other Biden priorities like voting rights, it became quite the parlor game. Sinema’s Democratic partner in Senate obstruction, Joe Manchin, had the obvious excuse of representing one of the reddest states in the country. Sinema’s Arizona is a battleground state that is trending blue. The fact that her centrist Arizona Senate colleague Mark Kelly, who is up for reelection this very year,...