Sen. John McCain, Arizona Republican, early on was thought to be the frontrunner for the 2008 Republican presidential nomination. But by summer 2007, he had been written off as a has-been. His poorly funded, lackadaisical campaign nearly ensured that he was put out to pasture before the primary races even began.

While he faded, the media went gaga first over Sen. Barack Obama, Illinois Democrat, then former Sen. Fred Thompson, Tennessee Republican, and most recently former Arkansas Republican Gov. Mike Huckabee. Yet now the nearly forgotten Mr. McCain is surging back.

Compared to the flashy Mr. Obama or mannequin-like former North Carolina Democratic Sen. John Edwards, Mr. McCain still looks tired and pale on the trail — except when he nearly loses his explosive temper and turns beet-red.

Mr. McCain has survived malignant melanoma and at times his face still appears craggy and swollen. His shoulders seem frozen, the result of years of torture as a prisoner of war held by North Vietnamese communists. If he wins in November, Mr. McCain, at 72, would be the oldest to enter the presidency — and, unlike Ronald Reagan, he will look it.

Liberals once flirted with Mr. McCain as a maverick when he ran in the primaries against the more conservative George W. Bush in 2000 — but then they also assumed Vice President Al Gore would naturally succeed Bill Clinton in the general election.

Now, though, they have little good to say about him. Mr. McCain never gave up on the unpopular Iraq war, loudly calling for both the appointment of Gen. David Petraeus and a surge of additional troops. His promises to cut spending rather than raise taxes aren't exactly endearing to Democrats.

Conservatives can't even count all the ways they have soured on him. Libertarians were furious that the McCain-Feingold campaign-financing law impinged on unfettered political expression. Mr. McCain never supported Mr. Bush's massive tax cuts that spurred the economy. But he did team with Sen. Ted Kennedy, Massachusetts Democrat, to craft a comprehensive immigration bill that included de facto amnesty to illegal aliens.

The Christian Right opposed his support for human-embryo stem-cell research. On issues like global warming and shutting down the detention facility at Guantanamo Bay, Mr. McCain has sounded like Speaker of the House Nancy Pelosi, California Democrat, or Mr. Kennedy. Why, then, has this old warhorse trotted back into the Republican race?

There are a number of good reasons that transcend ideology, and they loom larger every month of this topsy-turvy campaign.

First, in a campaign year of crass political reinventions, Mr. McCain does not flip-flop. He seems to enjoy telling people what they don't want to hear. Apparently, at his age, and after what he went through in Vietnam, there is no reason to begin trimming the truth now.

To those more liberal, Mr. McCain insists the surge is working and we will secure Iraq — only to explain to conservatives why we can't, either practically or morally, deport all 11 million illegal aliens. He seems more opposed to pork barrel and deficit spending than doctrinaire conservatives.

Second, Mr. McCain has the most diverse experience of any of the candidates in either party. Sens. Obama and Hillary Clinton, New York Democrat, may bicker over whether being first lady or growing up in Indonesia is the better foreign-policy background. But no one would question Mr. McCain's far greater breadth of service: carrier aviator, combat pilot, wounded veteran, tortured while a prisoner of war for 5½ years, U.S. congressman and senator for a combined quarter-century, 2000 presidential candidate. The list goes on.

Third, we are still in a war on several fronts — as we were reminded recently by the assassination, likely by al Qaeda, of pro-American Pakistani Benazir Bhutto. Many of the other inexperienced candidates fumbled in their initial reactions to Mrs. Bhutto's murder.

Mr. Obama ludicrously associated her death with the Iraq war. Mr. Huckabee, in Jimmy Carter fashion, apologized to Pakistan for the assassination — although he did not explain why. Former New Mexico Gov. Bill Richardson demanded Mr. Musharraf step down — as if we can snap our fingers and choose nuclear Pakistan's leaders.

Mr. McCain in contrast kept his cool. He candidly admitted that the tragic loss of Mrs. Bhutto was a setback to American democratic objectives, while reminding us that a nuclear Islamist Pakistan is unstable and doesn't present America with any good choices. In this war, having a veteran fighter and savvy old statesman as commander in chief makes a lot of sense.

I don't know whether plain-speaking John McCain, who finished fourth in Iowa with 13 percent of the vote, will win the presidency. But so far he's proved the most experienced of the candidates, and he has run the most principled and honest of the campaigns. Other candidates may be younger, better financed and more charismatic; none has more earned America's trust.