Senate-race rivals split on pledge Sestak unwilling to promise his support if Specter wins.

Rep. Joe Sestak said Sunday that he wouldn't commit to supporting Sen. Arlen Specter if the incumbent won the Pennsylvania Democratic Senate primary, a sign of how bitter their race has become as well as a fresh worry for party leaders hoping to hold the seat in the fall.

In contrast, Specter declared that he would endorse Sestak if things did not go his way Tuesday, quickly adding that he was confident of a win.

The two combatants spoke back to back on CNN's State of the Union With Candy Crowley less than 48 hours before the polls open, and as both men barnstormed the state to make their final arguments.

"Sure, I'm going to support anyone against Pat Toomey," the likely Republican nominee, said Specter, who appeared second on the show. Losing "is not going to happen, but I will answer your question."

Sestak would not. "In a war, you always know you're going to succeed, and so I'm going to win, and I look forward to Sen. Specter's support after the 18th," he said. Pressed by Crowley, Sestak said, "Never deal with something that's not going to happen."

The Senate race - with its national implications, expense, and personal animosity - has drawn attention away from the more docile contest for governor, with six candidates in the two parties vying to succeed Gov. Rendell.

State Sen. Vincent Hughes endorsed Allegheny County Executive Dan Onorato in the Democratic primary for governor, making Hughes the first significant black politician in Philadelphia to break from the favorite son, State Sen. Anthony Williams. Onorato has been ahead in the polls, with Williams running second.

In a Muhlenberg College/Morning Call tracking poll released Sunday, Onorato led with 39 percent support, to 15 percent for Williams, 10 percent for Auditor General Jack Wagner, and 9 percent for Montgomery County Commissioner Joe Hoeffel. Twenty-six percent said they were undecided.

Sestak and Specter each drew 44 percent support, with 11 percent undecided.

The Muhlenberg results were based on interviews, conducted over four days, with 400 Democrats with a history of voting in primaries. The margin of error was plus or minus 5 percentage points.

The Senate candidates argued about who would be more electable against Toomey, who narrowly lost to Specter in the 2004 GOP primary.

In Media, in the heart of his House district, Sestak said that Specter would be "red meat" driving up GOP turnout in the fall, and that Democrats and independents wouldn't trust the party-switcher.