Democrat Joe Torsella is dropping out of the 2010 Pennsylvania Senate race, according to sources close to his campaign, leaving Sen. Arlen Specter (D., Pa.) without serious opposition in the primary.

A video of Torsella announcing his withdrawal to supporters will be posted on the campaign's website shortly.

Torsella, the former CEO of the National Constitution Center, entered the race in February. He began in political life as an aide to Gov. Rendell when the latter was mayor of Philadelphia, and enjoyed broad support from Rendell's network of fundraisers and the tacit encouragement of the governor himself.

But Specter decided to become a Democrat April 28, receiving the immediate endorsement of President Obama, Rendell and other figures of the party establishment. That would have made Torsella's path to the nomination difficult.

"I was initially reluctant to quit something that so many people had thrown themselves into, heart and soul," Torsella says in the videotape. "But now that the dust has settled, it's clear to me that the kind of campaign this would become is not the kind of campaign I – or you – signe dup for. It probably would be negative, personal and more about Sen. Specter's past than our common future – and that won't do Pennsylvania any good."