It may have seemed like a good idea to Mr. Cruz at the time. But after Paris, he finds himself with a national security agenda that is increasingly at odds with the public will. Florida’s Marco Rubio (who opposed the NSA bill) had fun this week reminding Americans of the stark foreign-policy differences between himself and the Texan, noting that Mr. Cruz has supported laws that “weaken U.S. intelligence.” Mr. Rubio, who has delivered at least 10 major foreign-policy addresses in the past few years, is running as the unabashed hawk, calling for robust new U.S. world leadership. Mr. Cruz may have walked himself into playing the counterpoint—a Rand Paul stand-in.

Mr. Cruz will certainly argue that he’s more hawkish than Mr. Paul. He has consistently criticized Mr. Obama for failing to demonstrate international leadership. Many of his votes are accompanied by disclaimers. He says, for instance, that he opposed the defense reauthorization bills because they didn’t contain language prohibiting the indefinite detention of citizens.

Yet after Paris, this approach risks looking feckless. Foreign policy requires guiding moral principles and consistency. If national security continues as a pressing theme, will voters put their faith in a candidate who is on record (whatever the nuance) against military spending, against intelligence capabilities, against a proactive stance in Syria? A candidate who even refuses to condemn secrets-leaker Edward Snowden?