Now that John McCain has found his political mojo following big wins in states such as New Hampshire and Florida, he faces his toughest challenge: defending the position of front-runner in what has essentially become a two-man race against Mitt Romney. Rudy Giuliani and Fred Thompson have quit, Mike Huckabee is fading, and Ron Paul is busy having tea and crumpets with the March Hare and the Mad Hatter.

The nomination is McCain’s to lose. The case he must make in the primaries will ultimately rest on his leadership qualities rather than on the promise that he will advance some particular agenda in the proper way.

We know a lot more about John McCain than we know about many politicians. We know the Arizona senator is a man of intelligence, honor and integrity. We also know that his dizzyingly unique array of positions on the issues arouses serious doubts in many Republican primary voters.

Nearly everyone disagrees strongly with the senator on something important.

McCain’s habit of pushing positions independently of and often against the prevailing political winds is both an asset and a liability for him. His support of Bush and the controversial war in Iraq even during the crises of 2006 and his liberal bent on environmental and immigration issues have both hurt and helped him depending on the public mood. At all times, however, McCain’s firm convictions have commanded respect, even in disagreement, across the political spectrum.

But respectful disagreement is still disagreement. The senator has given Republican primary voters many reasons to be wary of him over the years. To earn their votes, he must allay their fears.

The senator’s co-sponsorship of the McCain-Feingold campaign finance bill troubles many politically active Republicans. In their view, the bill attacks political free speech without actually improving the regulation of political fundraising. Understandably, these conservatives lay the blame squarely at McCain’s feet, and McCain has done little to reach out to them.

McCain’s opposes waterboarding and other means of “torturing” captured terrorists, partly on the grounds that it exposes our soldiers to mistreatment at the hands of the enemy. This makes no sense, since al-Qaida has proven its willingness to torture (or even behead) its captives whether or not we torture ours. McCain feels a deep and understandable antipathy for anything resembling torture because of his painful experiences as a prisoner of North Vietnamese communists. But if he is to articulate his personal aversion to harsh interrogations sensibly, he should stick to normative arguments.

McCain’s economic credentials are mixed. Although he is a leading critic of wasteful discretionary spending, socialist healthcare and a proponent of personal Social Security accounts, his inconsistency on tax issues and a propensity to score political points by taking cheap shots at the corporate world is worrisome.

It’s possible that McCain has spent too much time in government and has subconsciously internalized the sanctimonious arrogance that most career politicians and government bureaucrats display toward the business community.

Thankfully, he appears to be gradually steering himself away from that particular populist camp.

McCain is a complex mix of conservative and liberal, but that does not make him a moderate. Conservatives will never rally around McCain the way they rallied around Bush, nor will liberals hate him with comparable rancor.

A McCain presidency would constantly be taking flak from both sides, if only for his sticking to his guns: In the end, the only person who will agree with John McCain on every issue is John McCain.

And maybe that’s way it should be.

[Reach columnist Russ Wung at opinion@thedaily.washington.edu.]