The remarkable thing about John McCain's emergence as the main threat to George W. Bush's claim on the Republican presidential nomination is that McCain has done it not by some brilliant strategy but essentially by winging it.

True, he and his team of advisers made some early strategic judgments that have paid off well, but most of them were dictated by circumstances. Take the decision not to campaign for last August's Iowa straw poll or the upcoming Jan. 24 Iowa caucuses. It was essentially a money decision, impelled by the recognition that the two candidates with fat checkbooks and no spending limits, Bush and Steve Forbes, would also enjoy the two largest bases of organizational support in Iowa--establishment Republicans for the Texas governor and religious conservatives for the publisher.

That meant that no matter how much he invested in Iowa, McCain was unlikely to finish better than third. So he announced that he would not actively campaign there, ascribing the decision to a high-minded refusal to abandon his principled objection to ethanol subsidies, which Iowa corn growers are supposed to cherish. That gave McCain brownie points elsewhere, while still leaving him in a position where he may finish as high as he would have if he had spent time and money in the state.

The decision looked even better when three other candidates--Lamar Alexander, Dan Quayle and Elizabeth Dole--spent themselves out of the race by their heavy investments in Iowa. With them gone, McCain has Bush in a very even battle in New Hampshire, with no one else at all close.

The same logic that suggested skipping Iowa dictated an all-out McCain effort in the first two primaries of the year, New Hampshire's on Feb. 1 and South Carolina's on Feb. 19. Unless he can beat Bush in one or both of those, the contest will be effectively over--and he knows it.

What has propelled him into contention in those two states is almost all McCain's own doing. I happened to be traveling with the Arizona senator in New Hampshire the week the American bombing campaign in Kosovo began last March. No other reporters were making the circuit with him, so we were riding in the same small van all day. Each morning, McCain would come down from his hotel room, having updated himself on the situation with a phone call to an anonymous source at the Pentagon. And each day, the number of radio, television, newspaper and magazine outlets seeking his views on what the United States should do seemed to double. One aide fielded the incoming calls while the other drove, and McCain expounded continually, without script or notes, as we traveled from event to event.

No one prepped the candidate for these interviews, nor did anyone in my hearing suggest the right "political" spin to apply. McCain was winging it, but on the basis of a long military career and nearly two decades of involvement with defense issues on Capitol Hill.

The pattern that was set back in those dark-horse days has continued as McCain has risen in the polls and the press corps following him has grown. Now there is a nonstop, daylong press conference for the reporters who jam onto his campaign bus. No topics are forbidden and McCain rarely avoids a question.

It wears on his voice, but it does not appear to diminish his energy. Last week, however, instead of going dawn to dusk from town meeting to town meeting, with nary a pause between the reporters' questions and the voters' queries, McCain began taking some afternoons off.

Part of the time was spent preparing for the gantlet of debates in Iowa, New Hampshire, South Carolina and Michigan; part of it polishing the "major policy speeches" on taxes, budget policy and education that he plans to deliver in the next few days. The speeches come in part as a response to press demands for fresh material, but they also signal his recognition that as a serious challenger, he has to prepare more carefully on topics outside his past legislative focus. When he attempted a health care speech last month in South Carolina, a few basic questions revealed that he had not done much homework on the topic, and he does not want to be embarrassed again.

But, being John McCain, most hours of most days will find him just "winging it," taking risks few other candidates would expose themselves to. Most of those other candidates are either history--or trailing in the dust.