Tim Carney notices that Rand Paul has been directing many of his attacks at Rubio:

Paul’s answer on the Cruz question: “I’m more concerned with Marco Rubio.” Why? “There’s not a dime’s worth of difference between Marco Rubio and Hillary Clinton on foreign policy. They’ve been dead wrong for the past decade, and they have endangered their country.” This sounds more like a guy who’s running against Rubio’s foreign policy than like a guy who’s trying to win the nomination.

Carney is right that Cruz is a more obvious rival for the voters Paul wants to win over, but Rubio is much more useful to Paul as a foil than the other candidates. Since Lindsey Graham has always been irrelevant in the race, Rubio is the most competitive candidate with a record of reflexive interventionism and support for immigration “reform.” Like Cruz, Paul is hitting Rubio where he believes him to be weakest in order to emphasize his own views on foreign policy and national security on the reasonable assumption that there are many Republican voters that aren’t interested in a doctrinaire neoconservative as the nominee. In so doing, he may make Rubio seem unacceptable to conservative votes that might otherwise support the Floridian, and he may be able to regain some support in the early states by becoming a more vocal critic of the disastrous foreign policy agenda that Rubio favors. Now that Cruz has started going after Rubio’s foreign policy record as well, it makes even more sense for Paul to do this.

Paul isn’t going after Rubio because Rubio is the “real front-runner” (he definitely isn’t), but because Rubio best represents the unreformed, bankrupt Republican agenda that Paul still thinks he is well-positioned to challenge. It may not win Paul any primaries, but criticizing Rubio in this way offers him the best chance to win back some of the support he lost over the last two years.