Sen. Ted Cruz during a lunch with colleagues last week in Washington passed the hat for campaign cash, as the Texas Republican’s anxiety mounts about the unusually brisk challenge from Democratic Rep. Beto O’Rourke.

O’Rourke is raising money by the truckload — enough to compete in Texas, a big state with costly media markets. The development has forced Cruz to hunt for resources in unlikely places for a politician who built his national career on opposition to the party establishment: fellow lawmakers, political action committees, and wealthy Republican donors.