With a “friend” like Donald Trump, Ted Cruz may not need enemies.

The senator from Texas and Republican presidential candidate has plenty of the latter: He has dueled, often personally and bitterly, with his own party’s congressional leadership.

But it’s not Senate Majority Leader Mitch McConnell or former House Speaker John Boehner or anyone else from official Washington who has been making Cruz’s life difficult in recent days. Instead, it’s Trump, the fellow candidate in the 2016 race with whom Cruz has aligned himself most closely—refusing to criticize the mogul when other candidates sought to drive down Trump’s poll numbers.

In return, Trump has begun floating questions about Cruz’s Canadian birth, and whether it makes him ineligible for the presidency under the Constitution. Worse for Cruz, it started just as he was kicking off a six-day bus tour of Iowa—a state he’s hoping will springboard his campaign to a string of primary victories.

So instead of selling his own storyline each day, Cruz found himself arguing that his mother’s U.S. citizenship means he himself is a “natural-born” citizen—and in a matter of days seriously straining a months-old “be-nice-to-Trump” strategy designed to pick up the developer-turned-reality-TV-star’s supporters.

Does that mean Cruz made a mistake by refusing to rip Trump when other candidates started doing so?