Conservative presidential candidate Rick Santorum said his endorsement of then-Sen. Arlen Specter’s 1996 campaign for the White House was “a mistake” today.

The Pennsylvania Republican, who is grasping for his party’s nomination to run against President Barack Obama this year, said he supported Specter because the two hailed from the same state even though the two differ widely on social issues.

“I was his colleague in the United States Senate. He asked me to stand with him. That certainly wasn’t one of my prouder moments I look back on,” Santorum said on ABC’s “This Week.” “But look, you know, you work together as a team for the state of Pennsylvania.”

Santorum added, “I certainly knew that Arlen Specter was going nowhere. I certainly disagreed with a lot of things that he said.”

Specter, a moderate Republican who switched parties in 2009 and ultimately lost in the 2010 Senate Democratic primary, ran as a pro-abortion rights candidate for president in 1996. Santorum, a practicing Catholic, is a strong opponent of abortion and has made his social stances a centerpiece of his campaign for president this year.

In hindsight, Santorum said that supporting Specter’s improbable presidential campaign “was something I look back on and wish I hadn’t done.”