Tight-Lipped Sinema Rivals Manchin as Democrats’ Wild Card

Kyrsten Sinema likes to make a statement. The 44-year-old senior senator from Arizona wore brightly colored wigs in the Capitol last year after hair salons shuttered because of Covid-19. Voting in March on whether to increase the minimum wage to $15 an hour, the centrist Democrat riled progressives by giving a curtsy and a playful thumbs-down. And last month she posted a picture of herself on Instagram sipping sangria and sporting a gold ring adorned with a profane message intended, presumably, for her critics: “F--- Off.”

But when it comes to where she stands on the issues, Sinema—who holds ...