MIAMI — The four remaining Republican contenders for president avoided their customary clashes in the opening moments of a crucial Florida debate Thursday night, sticking instead to placid monologues about free trade and immigration.

Front-runner Donald Trump defended his practice of having his name-brand clothing line manufactured in China and other foreign countries, saying it doesn't mean he won't keep his promise to block American companies from shifting operations overseas at the expense of U.S. jobs.

“Nobody knows the system better than me,” Trump said in response to a question from CNN moderator Jake Tapper.

The New York billionaire also said he needed to hire foreign workers for his businesses in the U.S. at times, and, tellingly, none of his opponents took the opportunity to criticize him.

At a time when Trump is appealing to millions of voters by accusing China and Mexico of ripping off the U.S. on trade, Ohio Gov. John Kasich argued that free trade was important, so long as America cracks down on foreign countries that cheat.

“We don't want to lock the doors and pull the blinds and leave the world, because, frankly, if we do that, prices will go up, people will buy less, other people will be out of work,” he said.

Florida Sen. Marco Rubio, who had hammered Trump during the last GOP debate for hiring foreign workers, did not mention his rival when the topic came up. But he vowed to crack down on U.S. companies accused of abusing visa rules by hiring foreigners to replace American workers.

On immigration, Kasich tried to strike a contrast with Trump, without naming him. For the more than 11 million immigrants in the country illegally, Kasich said, “they get a path to legalization, not to citizenship,” unless they have committed a crime.

Unlike previous debates, the tone early Thursday night was subdued and businesslike:

“So far I cannot believe how civil it's been up here,” Trump said.

But not all of it was light.

Texas Sen. Ted Cruz, eager to cement his position as the party's last best alternative to Trump, did have a firm counter to his rival, saying flatly at one point: “His solutions don't work.”

In a meaty discussion of Social Security, Cruz and Rubio said they'd gradually raise the retirement age for younger workers to help stabilize the system and stave off financial disaster for the system.

Trump, in contrast, said he'd do “everything within my power not to touch Social Security, to leave it the way it is.”

The billionaire businessman couldn't resist taking a dig at Democrats, saying that he'd been watching them intensely on such issues — “even though it's a very, very boring thing to watch” — and that they weren't doing anything on Social Security.

Cruz said that the system was “careening toward insolvency” and that it would be irresponsible not to address that. Rubio said Trump's plan to save the system by reducing waste wouldn't work.

Eliminating all fraud and waste “is not enough,” he said. “The numbers don't add up.”

The debate at the University of Miami in Coral Gables, Fla., comes as Trump's opponents are trying to break his march to the GOP nomination just five days before crucial primaries in Florida, Ohio, Illinois, Missouri and North Carolina.

Most important are the winner-take-all contests in the home states of Rubio and Kasich. Each must win his home state to have any chance of becoming the GOP nominee.

Even if Rubio and Kasich win Tuesday, it could be difficult to overtake Trump in the delegate count after his victories in 15 of the first 24 contests.

Polls show Trump with an especially large lead in Florida. Despite heavy rhetorical and financial support from establishment Republicans, Rubio's campaign has foundered. After a dismal showing in four contests that yielded zero delegates this week, he has had to fend off speculation that he would withdraw from the race.

Noah Bierman reported from Miami and Michael Finnegan from Los Angeles. Associated Press contributed.

nbierman@tribpub.com