Former Vice President Walter Mondale took another rare step into Minnesota congressional elections Wednesday, penning a second letter of support for Michele Bachmann's challenger Tarryl Clark.

The letter hit inboxes ahead of a key fundraising filing deadline this evening, which will paint a picture of whether Clark has been able to keep her war chest competitive with Bachmann's.

One reason that's important for the Clark camp: Bachmann's take will include all of the donations received during her event with Sarah Palin earlier this spring.

Mondale made his first pitch for Clark in September, when he reasoned that "few campaigns present us with the opportunity to make as significant a change as in Minnesota's 6th Congressional District."

His letter on Wednesday made it clear that Bachmann's stature gives her significant armor. He asked supporters to make a contribution before midnight.

"It will take an unprecedented campaign to defeat Congresswoman Michele Bachmann," Mondale wrote. "Despite her unconscionable defense of BP, Bachmann enjoys a level of celebrity that makes her a formidable opponent. It will take all of us, working together, to restore responsible, responsive leadership in Congress."

Mondale mentioned Bachmann's BP comments twice, an indication that the Clark camp might make this a continuing theme of the campaign.