Plan A for Republican presidential front-runner George W. Bush was to sail above the fray. Then Arizona Sen. John McCain got hot in a couple of key states. Now it's on to Plan B.

Bush has begun to criticize McCain--gently, but firmly--on such issues as campaign finance reform and taxes in an effort to persuade primary voters that McCain is outside the Republican mainstream. The first shots were fired in a GOP debate here Monday night, and senior advisers to Bush said there is more to come.

It's a sort of political judo, in which Bush hopes to use McCain's weightiest asset--his reputation as a political maverick--to take him down. His rebel streak may help him in a state like New Hampshire, where independent voters can be the decisive factor. But the Bush camp hopes it could haunt him in the majority of states, where the nominating process is more firmly controlled by the party faithful.

McCain's strategy is to use a strong showing--maybe even a win--in New Hampshire's opening primary to create a surge in other states with large numbers of independents. Freewheeling California is the grand prize. Although McCain still trails Bush by huge margins in national polls, he is making major headway on his journey: McCain appears to have opened a slight lead in New Hampshire.

By highlighting points on which McCain strays from party orthodoxy, Bush is trying to build a firewall around New Hampshire--in the Iowa caucuses a week before the Granite State primary, for example, and in the South Carolina primary soon after. Even if McCain wins New Hampshire, the thinking goes, strong Bush victories before and after will prevent a spark from becoming a blaze.

And so in Monday's debate, Bush attacked McCain's pet cause, campaign finance reform, as a betrayal of the GOP. "Here's my worry with your plan," he told McCain. "It's going to hurt the Republican Party, John, and I'm worried for this reason."

McCain's efforts at campaign finance reform would eliminate big corporate "soft money" contributions--much of which goes to Republicans--while allowing labor unions to continue to raise big political bankrolls through mandatory deductions from members' paychecks. Without "paycheck protection" to limit the resources that labor can pour into the Democratic Party, Bush said, the McCain plan amounts to "unilateral disarmament."

"Our Republican Party and our conservative values don't have a shot," he said.

The idea of campaign finance reform is so popular that strong candidates have embraced it in both parties. Republican McCain and Democrat Bill Bradley plan an unusual joint appearance Thursday in New Hampshire to hail the cause. Still, Bush supporters believe the issue will hurt McCain among core Republicans.

"Our thinking," said media strategist Mark McKinnon, "is that when Republican Party voters focus on it they should know it's anathema to the party."

Bush also challenged McCain on taxes, suggesting that the senator's proposed cut is too small. As one adviser to the Texas governor put it: "Whoever's the most aggressive tax cutter finds a foothold among the Republican faithful."

In both the Bush and the McCain camps this week, there is a conviction that the GOP primary is now quite clearly a two-man race. And McCain seems perfectly content to continue building his strategy on a foundation of independent voters.

While Bush took the opportunity Monday night to discuss his religious faith--Christian conservatives are a key GOP constituency in both Iowa and South Carolina--McCain denounced pork-barrel spending, political fat cats and the ethanol subsidies dear to Iowa farmers. To one McCain supporter, Marshall Wittmann of the conservative Heritage Foundation, the Bush strategy seems "directed to Iowa and South Carolina; I think they've taken New Hampshire out of the equation. It's almost like a sign of panic."

Ordinarily, an appeal to the base of the party makes sense, Wittmann continued. "But this may be a very different primary electorate. People are voting on character, and traditional pandering might not work as well as it has in the past. Bush's approach to campaign finance was not whether it's good or bad for the country but whether it was good for the party. I'm not sure that works."

Sen. Chuck Hagel (R-Neb.), another McCain supporter, questioned the whole premise that McCain is insufficiently loyal to party principles. "Here's a guy who's about as Republican as you can get," he said. "Who was the one guy with Bob Dole [in 1996] as his [presidential] campaign was going down the tubes?"

But in coming weeks, a number of leading Republicans around the country are likely to join Bush in criticizing McCain's campaign finance reform efforts. The party juggernaut rolls to the aid of its chosen candidate.

And the juggernaut got a bit bigger today. Former Tennessee governor Lamar Alexander, who abandoned his presidential hopes in August after being crushed by Bush, announced that he will support the Texas governor.

"He earned my respect the old-fashioned way: He defeated me," said Alexander. At the news conference today announcing Alexander's endorsement, Bush promised that any attacking he may do in the coming weeks will be in a spirit of friendly competition. "It's going to be tight," he said of the race for the nomination. "But you know, I like a good fight. I like competition. . . . I expect there's probably going to be some pretty good battles."