When Steve Forbes endorsed Texas Gov. Rick Perry in October, Perry was still riding high in the polls and the magazine publisher and two-time GOP candidate appeared set to be one of the most influential economic advisers to a top White House contender. Now, with Perry buried in fourth place in national polls, Forbes could be forgiven for changing horses.

He hasn’t, and today he began a three-day swing through New Hampshire to campaign on Perry’s behalf.

Speaking at a luncheon at the Rotary Club, where previous guest speakers included a local choir and three Rotarians who had recently visited Pakistan, Forbes championed Perry’s flat-tax plan that he helped craft and took a few swipes at frontrunners Mitt Romney and Newt Gingrich.

Romney’s economic plan is “weak tea,” and Romney has failed to demonstrate he has a “conservative core,” not least because he told the Wall Street Journal over the weekend that he favors a flat tax, said Forbes, whose 1996 and 2000 presidential campaigns were based on his flat-tax plan. “That was news to me,” he quipped. “Six months ago he was still trashing it.”

He also expressed doubts about Gingrich’s ability to overcome some of his past statements and business relationships. Gingrich has “to show he can respond to criticisms of things like Freddie Mac,” he said. “And again that’s an example of, you’ve been hit with something, how do you respond? So far he’s not been able to respond very well to it.”