Sen. Ted Cruz, R-Texas, uncorked one of his starkest attacks against Donald Trump on Wednesday by describing him as a proponent of "socialized medicine."

"Donald Trump is calling for the same socialized medicine that Bernie Sanders is," Cruz told Fox News host Megyn Kelly during an episode of "The Kelly File." "Both of them are saying 'expand Obamacare,' to put the federal government in charge of every one of our healthcare, which will inevitably lead to rationing of care and seniors being denied needed care."

That's a sharp escalation of rhetoric from Cruz, who as recently as Saturday night chose not to mention Trump specifically while discussing "socialized medicine ... proposed by the Democrats or proposed by a Republican." Cruz's tougher language against Trump was unleashed with a little more than a week to go before the South Carolina GOP primary, which could ultimately be decided by the older retirees who have moved to coastal regions of the state in recent years.

Trump promised in September to pass an "un-Republican" healthcare plan that guaranteed all Americans would be insured and "the government's gonna pay for it." He has also promised to repeal Obamacare, although he stands by the pledge to provide government coverage to poor people.

"We're going to take care of people that are dying on the street because there will be a group of people that are not going to be able to even think in terms of private or anything else, and we're going to take care of those people," Trump said in the New Hampshire debate on Saturday.

Cruz's remarks indicate he sees that as a political vulnerability for Trump. "At the very last debate, he said if you, a Republican voter, don't support socialized medicine, then you are heartless, then you want to let people die in the streets," Cruz told Kelly. "You know what, we hear that kind of rhetoric all of the time from Hillary Clinton and Bernie Sanders. I don't think Republican voters are interested in a Republican candidate saying they are heartless if they don't want the government taking over medicine."