Liz Cheney, Vice President Dick Cheney's daughter and former co-chair of Fred Thompson's presidential campaign, has signed on as a senior foreign policy adviser to Mitt Romney's campaign.

Cheney, a State Department principal deputy assistant secretary who was responsible for Middle East and North Africa initiatives, could help blunt charges by John McCain that Romney is weak on foreign policy issues.

"I am proud to support Governor Romney. Throughout this campaign, he has distinguished himself as a leader who can guide our country with a clear vision for overcoming the threats we face today," Cheney said in a statement released by the campaign on Sunday.

"Dedicated to the success of our missions in Iraq and Afghanistan, Governor Romney is the only candidate who has outlined a comprehensive strategy for defeating the global Jihadist threat. I look forward to working with Governor Romney, because he is the leader our country needs," she continued.

The Cheney news comes one day after John McCain scored a big-name endorsement from Florida Gov. Charlie Crist, who is now touring with McCain through the Sunshine State ahead of Tuesday's primary.

A meet-and-greet with McCain and Crist was hastily scheduled at a Tampa diner to follow a McCain appearance on NBC's "Meet the Press" on Sunday. It was put on the calendar after Saturday night's surprise announcement during a Pinellas County Republican dinner that McCain attended.

Crist and McCain don't agree on several issues, most specifically national catastrophe insurance, which McCain says would be too costly for the nation to pay out every time Florida has a hurricane.

But while the two disagree about some matters, Crist paraphrased Ronald Reagan, who said that people are probably friends if they can agree 80 percent of the time. He added that he likes all the candidates, but McCain is "a true American hero."

The Crist endorsement is also a blow to Rudy Giuliani, who has been saying all along he would triumph in Florida, and has essentially skipped hard-core campaigning in other states, hoping that a Florida win would catapult him back to the top, where he sat several months ago.

Click here to read about how Crist's endorsement hurts Rudy Giuliani.

Giuliani said Sunday that he was surprised by Crist's backing of McCain, but he doesn't think Florida voters are going to be overwhelmed by one person's support of a candidate.

"The reality is, I was surprised by the governor's endorsement. But everybody endorses. ... We have a lot of support here in Florida. Mayors and people up and down the state,'"Giuliani said on CBS' "Face the Nation."

"Governor, senator, attorney general, mayor. We all have different endorsements, but in the long run, it's getting your message to the people of Florida. That's the most important thing," Giuliani continued.

But with Giuliani falling in the polls, dropping behind Mike Huckabee to fourth place in the latest Reuters/C-Span/Zogby poll, the former New York City mayor's strategy appears to be falling apart. The focus in Florida has now shifted to the battle between McCain and Romney, who are tied in the Reuters poll at 30 percent.

That battle has gotten nasty with McCain accusing Romney of committing to a specific timetable for withdrawing U.S. troops from Iraq, a claim Romney categorically denies.

"You know, I don't know why he's being dishonest but that's dishonest," Romney said Saturday. "To say I have a specific date is simply wrong and is dishonest and he should apologize."

The reference dates to an April 2007 comment in which Romney said that U.S. and Iraqi military and government leaders should plan benchmarks for removing troops but that those timetables should be kept secret so the enemy doesn't just lay in wait for a U.S. exit.

McCain responded to Romney's characterization of his remarks by saying he is not going to apologize.

"Governor Romney has said that maybe he thinks I should apologize for saying what is clearly on the record is his support for timetables for withdrawal. I think the apology is owed to the young men and women who are serving this nation in uniform, that we will not let them down in hard times or good. There's who the apology is owed to," he said.

McCain is trying to turn the discussion back to Iraq as polling indicates that Romney has surged in Florida while the discussion has focused on the economy, Romney's strong suit. Also hoping to catch up to Romney in Florida in order to stay competitive is Huckabee, who came to McCain's defense on Sunday.

"I've never seen John McCain say something that was just blatantly untrue. The reason that I'm aware of Mitt Romney's statement about the secret timetable is because that was originally proposed by a senator from my state, Senator Mark Pryor," Huckabee told "FOX News Sunday."

Huckabee then denied that he was trying to help McCain by going after Romney, perhaps to position himself in a would-be McCain administration.

"I don't have to slam John McCain. I think that presidential politics can be civil. I think people can have mutual respect for each other. John McCain and I have entered into this race both looking for the same job. I'm not looking to be on his ticket. I don't think he's looking to be on mine," he said.

"I think that the issue is that we have a civil approach to the presidential process. Neither of us have sought to win the office by cracking the kneecaps of the other. We've talked about what we want to do," he said.

FOX News' Bret Baier, Shannon Bream and Mosheh Oinounou contributed to this report.