WASHINGTON — Sen. John McCain, whose tensions with social conservatives have become a drag on his presidential campaign, is finding himself at war with another vocal element of the Republican Party's base: economic conservatives who favor tax cuts.
McCain's votes against President Bush's tax cuts in 2001 and 2003 infuriated them. He is being pressed to explain why he broke with an element of the Bush agenda that most of them consider an unqualified success.
In one exchange last month, McCain criticized a prominent anti-tax group called the Club for Growth, saying he wasn't sure what he and the group had in common. In response, the group demanded that McCain apologize for his tax votes, and it added in an Internet video, "We're not sure what we have in common either."
McCain is planning an address next week on his economic ideas.
McCain's leading rivals have taken advantage of the tensions. They are trying to woo economic conservatives uncertain about the Arizona senator.
The competition over tax and fiscal policy is shaping up to be a major point of distinction for leading Republican candidates.
Mitt Romney, the former Massachusetts governor, started airing a television ad in Iowa and New Hampshire last week that cast him as a budget hawk.
"If I'm elected president, I'm going to cap nondefense discretionary spending at inflation minus 1%.... And if Congress sends me a budget that exceeds that cap, I will veto that budget," he says in the ad.
Romney says he would cut capital gains taxes for middle-class investors, and aides say he would trim marginal and corporate tax rates.
Rudolph W. Giuliani, the former mayor of New York, says he cut taxes 23 times in the mostly Democratic city and turned a budget deficit into a surplus. Last month, Giuliani accepted the endorsement of Steve Forbes, who ran for president in 1996 and 2000 as an advocate of a flat tax, which aims to simplify the tax system by imposing a single rate. Giuliani said he liked the idea of a flat tax but it was not feasible.
The candidate who wins the tax debate could gain the allegiance of a crucial GOP bloc.
"After a couple of elections where social conservatism moved to the forefront of the party, this year -- because none of the candidates are perfect on those issues -- there's a lot of Republicans who are trying to make their decisions based on economics," said Republican strategist Frank Donatelli, a former advisor to President Reagan who supports McCain.
