Just as Sen. John McCain of Arizona appeared poised to become the presumptive Republican presidential nominee, he was reminded over the weekend that many Republican voters still have not climbed aboard his bandwagon.

McCain, who won enough delegates in the coast-to-coast primaries and caucuses on Tuesday to place him mathematically beyond the reach of his Republican rivals, suffered embarrassing losses in the Louisiana primary and the Kansas caucus on Saturday to Mike Huckabee, a former governor of Arkansas.

Huckabee, who brags that in college "I didn't major in math, I majored in miracles," also wrestled McCain to a virtual draw on Saturday in the Washington state primary. Party officials declared McCain the winner by several hundred votes.

The Huckabee campaign announced Sunday on its Web site that it would challenge the results of the Washington primary. At issue are 1,500 votes that the Huckabee campaign says were not counted.

Results of the weekend contests do not affect McCain's solid lead, or change the likelihood of his winning his party's nomination. But they underlined the thinness of support for him among religious and social conservatives, who make up the bulk of Huckabee's voters, and the dilemma that has dogged McCain's presidential aspirations since 2000: how to overcome the distrust he elicits from that core constituency within his own party while maintaining credibility as the unorthodox Republican whom moderates, independents and many Democrats like so much.

Before the elections on Saturday, McCain seemed ready to begin casting the net wide for those independent voters.

"We have to energize our base and yet continue to reach out because we know that the formula for success in most campaigns, as you know, is your base, independents and Reagan Democrats," McCain told reporters on a flight from Wichita to Seattle.

In an interview on "Fox News Sunday," President Bush proclaimed McCain a "true conservative" but added that there was still fence-mending to do with the party's conservative base.

"I think that if John is the nominee, he has got some convincing to do to convince people that he is a solid conservative," Bush said. "And I'll be glad to help him if he is the nominee."

McCain's strong showing on Tuesday forced Mitt Romney, a former Massachusetts governor, from the contest and left Huckabee as the last major hurdle standing between McCain and the nomination.

In Huckabee, McCain has found an opponent who is in some ways the best of rivals, and, in other ways, the worst of rivals.