Independent Sen. Kyrsten Sinema of Arizona announced Tuesday that she won’t run for a second term after her estrangement from the Democratic Party left her politically homeless and without a clear path to reelection. Sinema’s announcement comes after Senate Republicans blocked a bipartisan bill to help secure the U.S.-Mexico border and deliver military aid to Ukraine and Israel, which Sinema spent months negotiating. She’d hoped it would be a signature achievement addressing one of Washington’s most intractable challenges, as well as a powerful endorsement for her increasingly lonely view that cross-party dealmaking remains possible.