A common foe may not be an adequate basis for coalition, as recent events demonstrate. From the New York Times:
The alliance between Sen. Ted Cruz and Gov. John Kasich of Ohio, formed to deny Donald Trump the GOP presidential nomination, was already fraying almost to the point of irrelevance Monday, only hours after it was announced to great fanfare.
With the pact, in which the two candidates agreed to cede forthcoming primary states to each other — Kasich would, most crucially, stand down in Indiana’s primary on May 3 to give Cruz a better chance to defeat Trump there, while Cruz would leave Oregon and New Mexico to Kasich. It appeared to be a measure of last resort, but initially it seemed like a breakthrough.
Cruz trumpeted what he called the “big news” in Indiana, a state that appears pivotal to stopping Trump from winning a majority of delegates. “John Kasich has decided to pull out of Indiana to give us a head-to-head contest with Donald Trump,” the Texas senator said.
But at his own campaign stop in Philadelphia on Monday, Kasich tamped down Cruz’s triumphalism. Voters in Indiana, Kasich said, “ought to vote for me,” even if he would not be campaigning publicly there. He added, “I don’t see this as any big deal.”
For a strategy like this to work, either the Cruz or Kasich campaign would need to truly set aside their goal of securing the Republican nomination in favor of blocking Trump. So long as both camps believe they may ultimately prevail in a convention floor fight, the temptation to undermine each other will cripple any joint effort.