John McCain's journey from the slough of a near-bankrupt political campaign last summer to the summit of his party's nominee for president has been an improbable trek.

Now the challenge for the self-described maverick is how to continue to run a campaign that at times embraces and at others separates itself from the Bush administration and the GOP's most conservative elements.

McCain never has been accused of playing well with others. That nature attracts independents even as it worries the party's most conservative quarters.

Traditionally, Republican candidates campaign on familiar themes, including defense spending and tax cuts. But this is no ordinary year. Iraq weighs heavily on voters of both parties. Economic fears abound. The Democratic nominee will make history as the first black or woman to carry the party's banner.

The 2008 election will be won in the political center, among the independents, who have been McCain's more natural constituency. Yet the more he moves their way, the more restless the conservatives become. President Bush's endorsement last week represents part of an effort to shore up the unruly and distrustful GOP base behind McCain.

His selection of a running mate will indicate whether McCain sees victory in appealing to the base or the center. Another leadership test will be how he finesses his uncharacteristic embrace of GOP orthodoxy — like making permanent the Bush tax cuts, which he opposed as senator — in an election year whose dynamics suggest a possible course change.

We shall soon see. True, it's unlikely that the old Navy airman represents the GOP's long-term future. But he is the party's present and, most important, not its past. That's enough to give the Republicans a fighting chance this fall.