Sen. Claire McCaskill (D-Mo.) knocked Sen. Marco Rubio (R-Fla.) on Sunday for backing away from his push for comprehensive immigration reform, saying on ABC's "This Week" that he had "folded like a cheap shotgun."
Rubio, who announced his bid for president last week, has gotten heat from some conservatives for co-authoring an immigration reform bill that would allow some undocumented immigrants to eventually become citizens, along with ramping up border security and enforcement measures.
He then said in February that he'd since learned a comprehensive approach was the wrong one, and that border security should be done separately and before other reform.
McCaskill said, "He took a principled, courageous stand on immigration reform" while helping to draft the bipartisan bill that passed the Senate in 2013 -- but then dropped those principles.
"Then the minute his party's base starting chewing on about it, the minute Rush Limbaugh criticized him, he folded like a cheap shotgun," she said. "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."
McCaskill is backing Democrat and former Secretary of State Hillary Clinton for president.
Rubio said on CBS's "Face the Nation" in an interview that aired on Sunday that it was wrong to say he "walked away from" immigration reform.
"Well that's not an accurate assessment," he said. "What I'm saying to people is we can't do it in a massive piece of legislation, and I know because I tried. We understand that we have to deal with 12 million human beings that are in this country, that have been here longer than a decade. We know we have to deal with this. We are not prepared to deal with it until first you can prove to us that this will never happen again."
CBS's Bob Schieffer asked whether Rubio would sign the bill he helped write into law if he became president.
"Well that's a hypothetical that will never happen," Rubio said, reiterating he would first ask for border security and enforcement bills.
Sen. Lindsey Graham (R-S.C.), who is considering a run for president and is another author of the 2013 immigration bill, also referred to Rubio's shift on immigration Sunday in an interview with "Fox News Sunday." When he was asked to give his thoughts on Rubio, he threw in a slight dig while praising the senator.
"He embraced immigration reform," he said. "He seems to have backed off -- I'll let him explain why. I think comprehensive immigration reform, securing our border and dealing rationally with the 11 million [undocumented immigrants], is the only way you're going to solve this problem."
This post has been updated with Rubio's comments from "Face the Nation."