Santorum’s stint as a Rubio surrogate got off to a shaky start this morning. When pressed to name Rubio’s top accomplishment in the Senate, he couldn’t come up with one:

The former Pennsylvania senator, who dropped his presidential bid Wednesday, told co-hosts Joe Scarborough and Mika Brzezinski he was supporting Marco Rubio’s presidential campaign because the Florida senator is someone “who can work together with people.” But Santorum struggled to name one accomplishment Rubio has had in the Senate.

It’s a perfectly legitimate question to ask about a presidential candidate, and Santorum’s protests that the question wasn’t fair just made things look worse than they were. Complaining that Rubio is part of a do-nothing Congress and therefore hasn’t done anything isn’t much of an excuse. That just reminds people that Rubio is both relatively inexperienced and belongs to the most disliked institution in the country.

Santorum couldn’t come up with anything because there aren’t any accomplishments to be named. This isn’t a case where a new surrogate hasn’t been sufficiently briefed on the minutiae of a candidate’s record. There’s simply nothing that Santorum could have cited as an example, because Rubio doesn’t have any significant legislative accomplishments since he entered the Senate five years ago. Even Obama managed to join up with Richard Lugar on a serious piece of nonproliferation legislation during his brief time in the Senate. Rubio can’t point to anything comparable. Neither can his rival Ted Cruz, whose even shorter Senate career has been defined entirely by obstructionist theatrics.

Cruz is running almost entirely as an ideological message candidate, and Rubio is relying heavily on his biography and family history, and they have to do this because they and their supporters can’t identify any successes they’ve had in their current positions. Maybe voters won’t care about this, but insofar as it reinforces Rubio’s reputation for inexperience and failing to do his job it certainly can’t help. It also has to bring to mind the major piece of immigration legislation Rubio tried to push through before abandoning it. If things had gone as planned, Rubio’s biggest accomplishment in the Senate would have been an immigration bill that most Republicans rejected.