The following piece was produced by the Huffington Post's OffTheBus project.
This weekend, New Hampshire Democratic Governor John Lynch greeted McCain at a Hopkinton town hall forum.
Lynch told the crowd that he has "enormous respect and admiration for Senator McCain and all that he has done for all of us all over the country if not all over the world."
The Arizona Senator said, "I'm a great admirer of the Governor's." He added, "America needs more of what you've done here in the State of New Hampshire."
Last week, a poll showed New Hampshire Republicans giving John Lynch a 60 percent approval rating.
In response to Lynch's appearance with McCain, Mitt Romney's New Hampshire campaign director, Jim Merrill, issued a statement that said, "Only John McCain would criticize a fellow Republican one day and then campaign with a Democrat the next."
Merrill was referring to when McCain told a crowd of Republican activists, "As we all know when he (Romney) ran for office in Massachusetts being a Republican wasn't much of a priority for him."
"But New Hampshire Republicans know all too well, what Governor Lynch's vision for change has meant for New Hampshire. We need the conservative change in Washington that can only come from Governor Romney," Merrill added.
The McCain camp countered with its own statement from their Granite State campaign chair, former Executive Councilor Peter Spaulding.
"John McCain learned from his political hero Ronald Reagan to extend his hand in friendship to members of the other political party. Obviously Mitt Romney never learned that lesson because he admitted he was never part of the Reagan Revolution, going so far as to reject the Reagan legacy and run to the left of Ted Kennedy," Spaulding wrote.
This tit-for-tat has been boiling for the past couple of weeks.
Dante Scala, a political science professor at University of New Hampshire-Durham, said, "I think this is the latest in a feud between the two that started at the UNH debate."
Scala added, "In the spring, Romney was challenging McCain who was the front-runner. Now the roles are reversed and Romney's getting a taste of his medicine."
Who will this benefit?
"Whenever a front-runner responds to a challenger, it's a good day for the challenger," Scala said.
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