John McCain's Debate Advice for Donald Trump's Opponents Republicans should resist the urge to gang up on Trump, he says.

 -- Former presidential candidate John McCain has some debate advice for the GOP candidates sparring with Republican presidential frontrunner Donald Trump: Stick to your message.

"Answer the questions," Sen. John McCain, R-Arizona, said in a moderated discussion Saturday at the Aspen Institute.

"Do not ... not so much ignore something like a direct attack, you don't want to totally ignore him, but get your message out," he said.

Trump, who leads the crowded Republican field in several recent polls, recently said the Arizona senator, a former prisoner-of-war in Vietnam, was only considered a hero because he was captured.

Trump has also lashed out at his Republican opponents, including former Texas Gov. Rick Perry, former Florida Gov. Jeb Bush and Wisconsin Gov. Scott Walker.

McCain, a two-time presidential candidate and the Republican nominee in 2008, suggested the other Republicans resist the urge to try to corner Trump.

"If you gang up on Donald Trump, then obviously you're going to have sympathy for him," he said.

Trump is on pace to qualify for the first GOP presidential debate on August 6. But he has also suggested he could mount an independent bid for president, which McCain said would be "incredibly damaging" to the GOP.

"I don't think there's any doubt that if he took 10 percent out of he Republican vote, that would be very, very difficult to overcome," McCain said.