AMES, Iowa—Sen. Ted Cruz typically begins his speeches with a couple of jokes. Lots of politicians do this; Cruz frequently quotes something from out of the mouth of his adorable kids, or from Jay Leno. Actually, Cruz does a decent impression of Leno's nasal wise-guy act.

Here at the Family Leadership Summit, Cruz opened with the standby joke that he was pleased to be out of Washington and "back in America," and reported that he'd eaten a pork chop on a stick at the state fair.

"It brought to mind a new diet that is all the rage in Washington," said Cruz. "It's the Obama diet. It works very, very well. All you do is, every day, you let Putin eat your lunch."

I wondered if Cruz had used this before, and discovered the origin of the joke—a Jay Leno monologue, nearly 11 months ago. In this unforgiving era of Google, where pols are nailed for plagiarizing lines and grafs, I assume Cruz either forgot to credit Leno or assumed that his audience was aware of the witticism. (Previously, Rick Santorum had declared that he was "not Karnac," and most of the crowd laughed, so the demographics were definitely Tonight Show-friendly.)