Sen. Claire McCaskill took a whack at her colleague, Sen. Marco Rubio on ABC's This Week when asked to respond to him calling Hillary Clinton "a leader from yesterday" during his own 2016 announcement earlier this week.

RADDATZ: Your reaction to that, Senator?

MCCASKILL: Listen, there is -- if you look at Marco Rubio's record, he took a principled, courageous stand on immigration reform and we passed a comprehensive bill in the Senate. And then the minute his pol -- party's base starting chewing on about it, the minute Rush Limbaugh criticized him, he folded like a cheap shotgun.

That's old politics. That's not what we need right now. That is the stalest trick in the book. That is shirking on your principles because of the political necessities of your party.

So I don't think that he necessarily represents some generational change. It sounds like, to me, old style politics.