Donald Trump speaks at the Republican U.S. presidential candidates debate sponsored by CBS News and the Republican National Committee in Greenville, S.C., on Feb. 13. (Jonathan Ernst/Reuters)

Donald Trump and Ted Cruz trained their sights on one other ahead of the South Carolina primary, where Trump maintains a strong lead over the rest of the Republican presidential field.

In several Sunday show appearances, Trump described Cruz, currently running in second place in South Carolina, as a major proponent for the 2005 confirmation of Supreme Court Justice John Roberts, a juror who conservatives resent for his decisions maintaining President Obama's health care law.

The issue of Supreme Court nominations has become central to the Republican primary over the past 24 hours since the unexpected death of Justice Antonin Scalia created a vacancy on the court.

"Justice John Roberts gave us Obamacare twice," Trump said during an interview with ABC's "This Week." "He could have foiled, he could have ended Obamacare twice. He got there because Ted Cruz pushed him like wild. ... Cruz shouldn't be talking because that was among the worst appointments I've ever seen. We have Obamacare because of Ted Cruz, Jeb Bush and George Bush."

Trump also slammed Cruz's personality, noting that he has no endorsements in the Senate.

"No endorsements, no support — he's a lone wolf. He's going to get nothing done, he's not a leader, he's never employed anybody, never created a job," Trump said. "He's a nasty guy, no matter how you figure it, he's a nasty guy."

Cruz returned fire Sunday morning, arguing Trump would appoint liberal justices to the high court opposed to gun rights.

"If Donald Trump becomes president, the Second Amendment will be written out of the Constitution because it is abundantly clear that Donald Trump is not a conservative," Cruz said on ABC in a direct appeal to South Carolina veterans.

"He will not invest the capital to confirm a conservative, so the result will be the same whether it’s Hillary [Clinton], Bernie [Sanders] or Donald Trump," Cruz said. "The Second Amendment will go away."