Travelers' advisory: Beware of Approaching Metaphors.

The Santorum campaign bus was barreling up and down the hills leading to Jefferson County when a sharp crack split the steamy morning.

Even before its wobbly thrump-thrump-thrump confirmed that a tire was flat, forcing the colorful conveyance to the side of the road, the RV's air conditioning had failed in the near-90-degree heat.

Not for the first time in his re-election campaign, Rick Santorum was confounded by forces beyond his control.

The senator, his wife, Karen, and their six children, whose pictures adorn the now-crippled RV, scrambled to places in trailing cars and soldiered on through a campaign day that took them to three widely spaced Western Pennsylvania appearances.

The journey offered loads of facile symbolism for Mr. Santorum's uphill quest. By Nov. 8, one of yesterday's omens will be validated as an emblem of the election: either the crippled campaign bus, or its occupants' perseverance.

Embarking on a late-summer bus tour, the Republican assailed his challenger, Bob Casey, before a series of small but friendly audiences. His remarks mixed ideology with classic pork-barrel appeals as he reminded each crowd of the government grants and projects that he had helped shepherd to their counties during his two terms in the Senate.

The tour had kicked off the previous evening with a North Park rally where roughly 300 Santorum partisans cheered him and the Oak Ridge Boys, the venerable country band that followed him to the stage facing the North Park pool.

As he has throughout the campaign, Mr. Santorum said the Democratic challenger was not offering adequate details on his policy positions, while claiming that he was trying to win election on the strength of the Casey name, a proven commodity in Pennsylvania politics.

"He doesn't tell you anything about what he believes and wants to hide behind his name to get elected," Mr. Santorum charged.

Yesterday morning, before a crowd of about 100 at the West Kittanning Fire Department, Mr. Santorum again assailed Mr. Casey's statement that he would have voted for an immigration bill that passed the Senate with the support of a variety of lawmakers, including Sens. Ted Kennedy, D-Mass., and John McCain, R-Ariz.

Mr. Santorum characterized both the legislation and his opponent as threats to national security because of what he and other critics have called a lack of adequate emphasis on border security and provisions to allow many illegal immigrants to attain citizenship in years to come, provisions derided as amnesty by Mr. Santorum.

He said the immigration bill was an example of the "dangerous position'' taken by his rival.

At another point, while arguing that "Islamic fascism" posed a threat that the nation cannot ignore, he said "folks like Bob Casey and [Democratic National Chairman] Howard Dean don't understand. ... If they did they wouldn't be talking about withdrawing troops and all the rest.''

Larry Smar, a spokesman for the Casey campaign, maintained that Mr. Santorum misstated the Democrat's positions, saying that Mr. Casey had never spoken in favor of a troop withdrawal or a timetable for withdrawal from Iraq. He also took exception to Mr. Santorum's claim, delivered before a knot of listeners in a barn at the Butler Farm Show, that Mr. Casey had advocated ratification of the Kyoto Treaty, a mandatory reduction on emission of greenhouse gases that was rejected by the United States in President George W. Bush's first term.

"He's so dangerous and so extreme on these issues,'' Mr. Santorum said.

"That's a lie,'' Mr. Smar said. "Rick Santorum has, throughout this campaign, had no regard for the truth ... [this] is another example of Santorum saying things with no facts to back it up. Bob did not say that he would vote for Kyoto. It's just one more in a series of untrue attacks.''

Defending her candidate's assertions, Mr. Santorum's press secretary, Virginia Davis, pointed to a passage in a June article in the Johnstown Tribune-Democrat that reported that "Casey said he doesn't believe U.S. troops should be removed from Iraq immediately but should be by the end of the year.''

"As for Kyoto,'' Ms. Davis said in an e-mail, "Casey said in The Philadelphia Inquirer that he supports the positions of the League of Conservation Voters. LCV supports the Kyoto Treaty."

Mr. Smar said the Tribune-Democrat article cited by Ms. Davis had incorrectly described Mr. Casey's position and noted that the paper had subsequently printed a clarification to that effect. He said that the while the League of Conservation Voters had indeed endorsed Mr. Casey, that did not mean that the Democrat agreed with each and every one of the League's positions, or those of any other group that might endorse him.

Mr. Smar also insisted that Mr. Casey had offered detailed positions on a variety of issues, rejecting the broader Santorum charge that the Democrat had been vague on policy details.

On one issue before Congress last week, Mr. Santorum criticized Democrats for rejecting a measure that would have paired a minimum wage hike with a permanent reduction in estate taxes. He called the measure a reasonable compromise and noted that it also included mine reclamation provisions valuable to Pennsylvania that he had been instrumental in including in the bill.

Mr. Santorum's bus tour set off in the wake of a new poll that showed a narrowing of the gap that he has faced since the beginning of the race. Mr. Casey has enjoyed a consistent lead in the low double digits in almost every public poll, but a new survey by Muhlenberg University and the Allentown Morning Call, released Sunday, put the Republican's deficit at only six points, 45 percent to 39 percent.

While the 39 percent figure is a dangerously low number for any incumbent, the survey depicted a closer contest than any other recent poll. A Rasmussen survey released last week depicted Mr. Casey with a margin of 50 percent to 39 percent in a two-way race with the incumbent.

No public poll has yet tested the race as a three-way contest including Carl Romanelli, the Green Party candidate who, with crucial Republican support, submitted nominating petitions last week which he said included well over the 67,000 signatures needed to secure a spot on the November ballot.