After leaving this to surrogates for a couple days, the Obama campaign is ratcheting up the pressure on onetime Hillary chief strategist to ax Mark Penn once and for all, in the apparent hope that keeping Penn front and center will weaken her grip on her base of blue collar voters in Pennsylvania and other remaining states.

On an Obama campaign conference call moments ago, the Obama camp rolled out high-profile labor supporter James Hoffa, the president of the International Brotherhood of Teamsters, who called on the Clinton camp to end Penn's association completely.

"You can't have a guy on your payroll who's lobbying for Colombia," Hoffa said, adding that it was time for her to "end his services completely." He blasted Penn for "taking money from a foreign nation" to boost the free trade agreement that "she says she's going to vote against."

Hoffa added that Penn was a continuing drain on Hillary's "credibility," claiming that Penn is "still calling the shots," which is certainly debatable -- while Penn is still playing a role, obviously, Geoff Garin has taken over as senior strategist.

One other interesting nugget from the call: Hoffa referred to some internal polling that he claimed showed that Obama's race was not resonating as an issue among union members.