MIAMI — Donald Trump went all out to appear presidential in the 12th GOP debate — speaking in firm but level tones, eschewing insults and patiently refusing to take the bait when his rivals tried to goad him into losing his temper.

“We’re all in this together. We’re going to come up with solutions. We’re going to find the answers to things, and, so far, I cannot believe how civil it’s been up here,” the GOP front-runner said a half-hour into the face-off in Miami Thursday night.

He also offered more detailed positions on Social Security, Israel, ISIS and Cuba, and avoided the harsh rhetoric that marked his rallies and previous debates.

And despite sharp attacks by Sens. Ted Cruz and Marco Rubio, the contest never degenerated into the raucous mudfests of past debates, when the candidates insulted and talked over one another.

When Trump said he would try to not make short-term changes to save Social Security, Cruz pounced, saying, “That is the statement of a liberal who doesn’t understand government is the problem.”

Trump refused to be drawn in.

He called himself a strong supporter of Israel and said he would strengthen the US military to destroy ISIS.

“We have to knock out ISIS, get rid of it and then come back and rebuild our country, which is falling apart. I would listen to the generals, [but now] we’re not allowed to fight. We’re not knocking out the oil because they don’t want to create environmental pollution up in the air. We don’t fight like we used to fight. We used to fight to win,” he said.

Trump also stood by comments from a day earlier when he told CNN that Muslims hate America.

“I will tell you there’s something going on that maybe you don’t know about . . . but there’s tremendous hatred, and I will stick with exactly what I said,” Trump replied.

“I don’t want to be politically correct. I like to solve problems. We have a serious, serious problem of hate. All across the Middle East, you have people chanting, ‘Death to the USA.’ That does not sound like a friendly act to me.”

Rubio had a zinging comeback.

“I’m not interested in being politically correct; I’m interested in being correct,” he said.

He slammed Trump for his support of opening relations with Cuba, saying its Communist dictatorship made no concessions in the deal brokered by the Obama administration. Trump replied that the US needed “a much better deal.”

“We don’t have people making good deals. We don’t have a clue. [But] I do agree something [to improve relations] should take place. After 50 years, it’s enough time, folks,” Trump said.

Rubio got the loudest applause of the night from his hometown crowd by demanding policies that would signal an end to the Castro regime.

In the end, there were no clear game-changing moments as the candidates head into five critical primaries next week that could determine the GOP nominee.

In his closing statement, Trump looked to the general election.

“The Republican Party has a great chance to embrace millions of people that it’s never known before,” he said. “We should seize that chance.”