Poole said in an essay that there are no true moderates left in the House of Representatives, and just a handful remaining in the Senate, in contrast to the Reagan era when about half of the members of Congress could be described as moderates.
For Specter, the benefit of crossing party lines wasn't always about being true to his convictions. He also used it to benefit the causes he championed.
"He was a master politician," Rendell said. "He was as smart as a whip."
In his 2004 run for re-election, Specter was endorsed by both the AFL-CIO of Pennsylvania and the arch-conservative Rick Santorum, then Pennsylvania's junior senator. Santorum later said Specter had pledged to support then-President George W. Bush's nominees to the Supreme Court, regardless of their views on abortion rights. Specter, who supported abortion rights, had said he never would make such a promise under any circumstance.
In 2001, he voted for Bush's package of tax cuts, but voted with Democrats to route $450 billion into education and debt reduction. He negotiated $10 billion for medical research when he agreed to vote for the stimulus.
Specter, who grew up in Depression-era Kansas, justified his vote for the stimulus as the only way to keep America from sliding into another depression.
But Specter had barely won his 2004 Republican primary and decided that the stimulus vote had ensured his political career would not survive another GOP primary. At the urging of good friends Vice President Joe Biden and Rendell, both Democrats, he switched parties.
Still, many Democratic primary voters had never voted for Specter, and they weren't about to start.