As Barack Obama traveled overseas, the campaign against him appeared to take a decisive new turn when John McCain zeroed in on his Democratic opponent’s character.

In a year when polls show an easy victory for a generic Democratic candidate, McCain has until now been loath to employ the tack many strategists see as essential and which anonymous e-mailers and commenters with no apparent links to his campaign have been practicing since last summer: hitting Obama not on his record or his platform, but on his values and person.

The Democrat’s Achilles’ heel in this model is an inchoate sense among some voters that the new arrival on the national stage with the unusual biography — who’s the first black nominee from either party — isn’t American enough.

Prior to Obama’s trip overseas, though, McCain had instead employed, without appreciable effect, a more conventional critique of his opponent as an ordinary politician, a flip-flopper and, of course, a liberal.

On Saturday, though, McCain released a new television advertisement in which the announcer says that on his trip, Obama “made time to go to the gym, but canceled a visit with wounded troops. Seems the Pentagon wouldn't allow him to bring cameras.”

"John McCain is always there for our troops," adds the announcer, before concluding with the campaign’s new slogan: “McCain, country first.”

The slogan’s inverse implication for his opponent was made clear earlier in the week, when McCain accused Obama of placing the his political ambitions before the national interest.

"It seems to me that Obama would rather lose a war in order to win a political campaign," McCain said Tuesday in New Hampshire, a line he’s been using regularly since.

While Republican presidential candidates have long sought to paint their Democrat foes as insufficiently devoted to the country, the military or both, McCain’s suggestion that Obama preferred to hit the gym than to visit wounded soldiers is considerably more personal than, say, President Bush’s 2004 attack on Sen. John F. Kerry for voting against bills to fund troops in Iraq. In some ways, it bears more of a resemblance to the third-party Swift Boat campaign that denigrated Kerry’s service in Vietnam.

Further, McCain is uniquely qualified to make this charge, and Obama is uniquely vulnerable to it.

A former naval aviator and prisoner of war in Vietnam, McCain is pressing his case against a candidate with no military experience — thanks in part to a subterranean smear campaign that’s tapped a nerve with some voters who don’t see Obama as entirely American.

While the botched troop visit might have been the stuff of an attack ad in any case, since it was the only significant slip-up in an otherwise well-staged trip, McCain’s new ad dovetailed with the latest viral e-mail aimed at Obama, a widely circulated — though later recanted — missive from a Utah National Guard officer stationed in Afghanistan, Joseph Porter, who wrote that Obama "blew ... off" and "shunned" soldiers during his visit there.

"He was just here to make a showing for the Americans back home," Porter wrote, though press reports contradicted some of the details provided in his e-mail. "It was almost that he was scared to be around those that provide the freedom for him and our great country."

Obama responded with high-minded disappointment to McCain's new round of attacks, and his traveling companions in the Middle East, Republican Sen. Chuck Hagel of Nebraska and Democratic Sen. Jack Reed of Rhode Island, condemned them.