President Obama swept into Philadelphia yesterday to help newly minted Democratic Sen. Arlen Specter raise nearly $2.5 million for his reelection campaign, inserting the White House directly into a primary battle.

"I'm going to need all of you to redouble your efforts in the months to come to fight for Arlen, because he's fighting for you, and he's fighting for what's right," Obama told about 200 big-ticket donors at a private dinner at the Convention Center.

"It's not easy, because we live in a polarized environment, and politics has become sport," Obama said, "and it's hard to sustain complex arguments about why we have to make choices that don't always seem real attractive on the surface." Specter's crucial vote for the stimulus package, he added, helped pull the economy from the brink.

Specter, speaking before Obama, praised the president for attacking problems from the economy to health care and global warming, and he mused about the political mood of the country.

"It's a very curious election - there's an enormous amount of anger out there," Specter said. "Nobody is safe."

As the national leader of the Democratic Party, Obama could have stayed out of the struggle between Specter and Rep. Joe Sestak (D., Pa.), but senior White House officials have said the president intends to help incumbent Democratic senators win in next year's midterm elections.

Specter was invited to the White House in April, the morning after the longtime Republican switched parties to avoid defeat in the 2010 GOP primary, and Obama promised to do whatever it took to help Specter win reelection.

Vice President Biden had played a leading role in persuading his old Amtrak-riding buddy to become a Democrat. Gov. Rendell and other leaders of the party establishment have also rallied around Specter, who has been in the Senate for 28 years.

Obama has expressed preferences in other intramural Democratic fights, notably Senate races in Colorado and New York.

Last night's take will be split between the Specter campaign and the Democratic Senatorial Campaign Committee. Event organizers are within "striking distance" of the goal of raising $2.5 million, Specter campaign manager Christopher Nicholas said last night.

To gain admittance to the private steak dinner - and get a posed picture with the president - guests had to donate $10,000 or raise $50,000 from others.

In the room was a who's who of Democratic fund-raising in Southeastern Pennsylvania. David L. Cohen, executive vice president of Comcast Corp. and former Rendell chief of staff, chaired the event. Others present included developer Ron Rubin and lawyers Mark Alderman, Steve Cozen, Tad Decker, Richard A. Sprague, Mark Aronchick, and Ken Jarin.

Before the dinner, about 500 donors attended a general reception elsewhere in the Convention Center, to which tickets cost $2,400. Obama spoke to that gathering, too, praising Specter as a "tough son of a gun."

In an unusual move, Senate Majority Leader Harry Reid (D., Nev.) scheduled no votes in his chamber after 3 p.m. yesterday so that Specter and Sen. Bob Casey (D., Pa.) could be in Philadelphia.

That gave Sestak an opening to blast Specter for hypocrisy. The incumbent's campaign has attacked Sestak for missing more than 100 votes in the House since he started running for the Senate.

"This gets to a larger issue, and why I am running against the establishment's wishes, because too often it favors the powerful and well-connected," Sestak said in a statement.

Former Sen. Rick Santorum (R., Pa.), who was crucial in helping Specter survive a 2004 challenge from the right, said his former colleague "has done a hard left turn to try and get into the good graces of this president, and obviously he is getting rewarded for that." Santorum spoke on a conference call arranged by the Republican National Committee.

Specter flew with Obama to Philadelphia aboard Air Force One from Pittsburgh, where both addressed hundreds of labor activists at the AFL-CIO convention. There, Specter took another step in his political evolution, saying he would support legislation making it easier to form unions.

As a Republican, Specter declared on the Senate floor that he could not vote for the Employee Free Choice Act because it would weaken the requirement for a secret ballot in union certification elections.

"We have pounded out an employees' choice bill which will meet labor's objectives" while preserving secret elections, Specter told cheering union delegates at the convention.

Specter also has emerged as a staunch defender of a government-run health-care plan to compete with private insurers, after earlier opposing it.

Obama's support of the establishment candidate seems ironic considering he won the party's nomination with an outsider message. Sestak is running the insurgent's campaign in this race.

A poll by Franklin & Marshall College in Lancaster last month showed Specter leading Sestak 37 percent to 11 percent among Democratic voters, with half undecided. But the poll also showed weakness for the party-switching Specter.

Pollsters asked Pennsylvania voters of all stripes whether Specter deserved another term or whether it was time for somebody else. Thirty-four percent indicated support for Specter's reelection, with 54 percent saying it was "time for a change."

When Air Force One landed in Philadelphia yesterday afternoon, Obama and Specter emerged from the cabin simultaneously, arms around each other's shoulders, waving and smiling for the cameras.

Specter no doubt hopes that Democratic primary voters see and remember that image.

Obama to Appear On Letterman

President Obama will visit David Letterman on Monday, part of a media blitz to sell his health-

care plan.

CBS said the visit would be the first ever by a sitting president to Letterman's Late Show. Obama has been on the show five times, most recently last September, during the campaign.

Obama is scheduled to appear on five Sunday morning talk shows

this weekend, on ABC, CBS, NBC, CNN, and Univision. That's a highly unusual schedule, even for a president eager to get his message across throughout the media.

- Associated Press

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Read the president's speeches from Ohio

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Contact staff writer Thomas Fitzgerald at 215-854-2718 or tfitzgerald@phillynews.com.