WASHINGTON—The split decision from Arizona and Utah on Tuesday leaves the Republican presidential race in the same place it has been: front-runner Donald Trump with a commanding lead, and Sen. Ted Cruz and the GOP establishment in a desperate effort to stop him from clinching the nomination outright.

Mr. Trump’s Arizona primary victory led to unlikely support Wednesday for Mr. Cruz, who won the Utah caucuses. The Texas senator, who built his campaign around how much he is hated by the Washington establishment, on Wednesday was...