Consumer activist Ralph Nader this week called for a primary challenge to President Barack Obama.

"I've heard from a lot of progressives that they want to do something to bring President Obama towards the left," Current's David Shuster told Nader Friday. "But what about the argument that a primary challenge to President Obama would hurt him, cause fissures in the Democratic Party and possibly impede the party efforts in the general election?"

"Just the reverse," Nader explained. "It will challenge him, bring the best out of him and there's nothing worse for a candidate in terms of lessening the enthusiastic level for him than to go through an unchallenged routine of repetitious primaries."

Watch this video from Current's Countdown with Keith Olbermann, broadcast July 29, 2011.