A year ago, Senator Arlen Specter was on the campaign trail in Pennsylvania — appearing for a fellow Republican senator,  John McCain, who was in an intense race for the presidency against a Democratic senator, Barack Obama. The two presidential candidates both spent a great deal of time in the swing state, which ended up going Democratic in the November election.

A year later, Specter is busy on the campaign trail again in another tough Philadelphia political battle, his own bid for reelection. But this time, the former moderate Republican is a Democrat. And he wielded the Democrats’ most formidable election weapon at an evening of fundraising on Tuesday — President Barack Obama.

Specter left the Republican party earlier this year, helping to strengthen the Democratic majority in Congress. To thank the 79-year-old, Obama had said he would stand by Specter even in a primary fight to be nominated as the Democratic candidate to retain his Senate seat in 2010.

And he stood by him on Tuesday. Obama spoke at two different fundraising events in Philadelphia. The Philadelphia Inquirer said the twin Specter events were expected to raise close to $2.5 million, the goal of the evening. Obama touted Specter’s record and qualities to an audience of several hundred supporters who had donated $1,000 to $4,800 each.  Slightly hoarse after a day of speeches to auto workers, the AFL-CIO and Specter supporters, Obama later spoke again at a sit-down dinner for a group of big donors to Specter and the Democratic Senatorial Campaign Committee.  Aides said Obama posed for 100 pictures with the 200 dinner attendees, two of them at a time.

Obama hailed Specter as “a man who has always put his state before politics, before party.”

Specter praised Obama as “a transformational candidate moving toward being a transformational president.”

Specter knows about transformation.

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PHOTO CREDITS: Specter and Obama arrive in Philadelphia, Larry Downing/REUTERS. McCain and Palin campaign in autumn 2008, Brian Snyder/REUTERS