TAMPA, Fla. — Republican presidential hopefuls plan to use a televised debate tonight to press frontrunner Rick Perry to justify his criticism of Social Security, which has dominated the contest in recent days.

Perry, the Texas governor, partly explained his remarks in an op-ed article in USA Today. In it he said his proposed changes would not affect current and soon-to-be retirees. Perry wrote that “reforms,” which he did not specify, are needed to shore up the program’s long-term health.

Former Massachusetts Gov. Mitt Romney, touting an endorsement from a former rival today, has sharply criticized Perry for calling Social Security’s funding arrangement a “Ponzi scheme” and “monstrous lie” in a California debate last week.

The government predicts that unless Social Security is modified it will be unable to fully fund benefits starting in 2037.

Romney is running second to Perry in recent polls of Republicans. The two men and six other candidates planned to face each other tonight in a two-hour debate sponsored by CNN and the Tea Party Express. The debate airs at 8 p.m. Eastern time.

Romney won an endorsement from former Minnesota Gov. Tim Pawlenty, who recently dropped out of the GOP contest. People close to Perry’s campaign said Louisiana Gov. Bobby Jindal would endorse the Texas governor and accompany him to Tampa.

Romney made an earlier stop today at Boeing Co.’s new $750 million plant in North Charleston, S.C. He criticized the Obama administration’s links to organized labor, arguing that a National Labor Relations Board’s complaint against the aeronautics giant is White House payback to unions.

Romney suggested that any economic stimulus package should include legislation telling the NLRB to drop its complaint against Boeing. The company is accused of retaliating against union actions in Washington state.