John McCain’s message to Newt Gingrich? Man up.

Former Massachusetts governor Mitt Romney (R) and Sen. John McCain (R-Ariz.). (Chip Somodevilla/Getty Images)

“You know, and I say to my friend, Newt, politics isn’t beanbag; it’s a tough business,” McCain told Fox News Channel’s Sean Hannity Wednesday night. “And I respect Newt’s record. I don’t agree with a lot of the things that he did. But at the same time, I understand why he might be a little upset, and he sounds very upset. But that isn’t the way you win elections. The way you win elections is to come forward with your own positive agenda, which is exactly what Mitt has been doing all along.”

(McCain was quoting a grammatically cleaned-up version of 19th century political satirist Finley Peter Dunne’s phrase, “Politics ain’t beanbag.”)

McCain, who on Wednesday announced his endorsement of Gingrich’s rival for the GOP nomination, former Massachusetts governor Mitt Romney, was responding to a radio interview with Hannity earlier in the day in which Gingrich tore into Romney’s record and the negative ads run by a super PAC supporting him.

“He’s somebody who is not candid,” Gingrich said of Romney. “He is not candid about his record, he’s not candid about his PAC; his PAC runs ads that are false. They have spent millions of dollars and I suspect they will pivot now and go after Rick Santorum because the only technique they have is to try to shrink the other candidate.”

In the radio interview, Gingrich also echoed a Democratic line about Romney’s support within the Republican Party, arguing that “after five years of campaigning, they can’t move Romney above 25 percent.”

“He got basically exactly the same vote in 2012 that he got in 2008,” Gingrich told Hannity. “And so, millions of dollars of campaigning later, he is trapped with three-fourths of the Republican Party rejecting him because he is a Massachusetts moderate.”

Asked by Hannity about that criticism Wednesday night, McCain replied that “it’s pretty obvious from the tone of his voice that Newt Gingrich is very unhappy.”

“He was sitting very well for a period of time,” McCain said of Gingrich. “He kind of had a succession of people who have gone up and then gone down, while Mitt has been putting one foot ahead of the other and maintaining a steady strength and has been going up. He is going to do well here in New Hampshire. And I am confident he will do well in South Carolina and in Florida. And again, to say that the Iowa caucuses, who were something that was expected, it was not. I mean, it shows that the campaign has been gaining traction.”

McCain also said that he thought the 2012 will be much “nastier” than the 2008 race – but due to the Obama campaign, not to any of the GOP contenders.

“If you think the 2008 campaign was nasty, you wait and see the kind of campaign that the Obama campaign have already announced that they are going to run,” he said. “And we got to be prepared for that. And I guarantee you, all of us will be fighting back. The future of this country now rests on this election.”