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.

Huckabee, an ordained minister, has avoided negative campaigning as a general rule, and has been almost scrupulous in treating McCain with respect. At a point where public attention to the all-but-settled Republican presidential contest might have lagged, Huckabee's feisty competitiveness guarantees that that will not happen.

On the other hand, while it is unlikely that Huckabee will win, he can bloody McCain before the political bout is decided.

When Huckabee told an audience at the Conservative Political Action Conference last week that he favored a constitutional amendment banning abortion, and an amendment defining marriage as the union of a man and woman, the wall-shaking roar of the crowd was as much a rebuke of McCain, who has declined to support both proposals, as it was support for the speaker.

Huckabee followed up that appearance with a visit on Sunday to the late Jerry Falwell's church in Lynchburg, Va. In an address to the congregation, Huckabee marveled at "what an incredible influence" Falwell "had in this country," and he stressed how fond he had always been of the man who founded the Moral Majority. He did not have to remind any of the 6,000 parishioners of what some others, particularly McCain, might have said in the past about their late pastor.

To the delight of his supporters, Huckabee has insisted that he intends to press on with his campaign, despite the delegate count weighing heavily against him.

"His supporters are true believers who don't care so much about pragmatic considerations," said Todd Harris, who served as communications director for the campaign of former Tennessee Sen. Fred D. Thompson. "They believe he has a message and that that message should be heard. And as long as they keep sending him money it will be."

As if to reinforce that notion, Huckabee's campaign vowed Sunday that he "will be exploring all available legal options" regarding the outcome on Saturday in Washington state.

"The Huckabee campaign is deeply disturbed by the obvious irregularities in the Washington state Republican precinct caucuses," the campaign's chairman, Ed Rollins, said in a statement. "It is very unfortunate that the Washington state party chairman, Luke Esser, chose to call the race for John McCain after only 87 percent of the vote was counted."

On his campaign plane on Friday, McCain said he understood the continuing skepticism of some conservatives toward his candidacy — a skepticism most bitterly voiced by a platoon of conservative radio talk show hosts like Rush Limbaugh and Hugh Hewitt. But he said he has been making overtures to conservatives, and will continue to do so.

"Look, after 2000, there were a lot of McCainiacs who were very angry and bitter," he said, referring to a bruising loss he suffered to Bush in South Carolina. "And after President Bush and I got together, I worked very hard to say, look — you know, a lot of people were bitter about South Carolina, a lot of people were bitter because, you know, when you invest your hard work and your effort and your passion into a candidate. I understand that there was a period there where you've got to unify people and get them to recognize what the major goal is."