WASHINGTON -- Former Rep. Barney Frank has gained the backing of two of the most influential online progressive groups in his bid to be appointed to Sen. John Kerry's soon-to-be vacated Senate seat. Both MoveOn.org and the Progressive Change Campaign Committee (PCCC) have begun online petitions supporting Frank as the interim replacement for his fellow Massachusetts Democrat.

If Kerry is confirmed as President Barack Obama's next secretary of state, which is expected, Massachusetts law stipulates that it's up to the governor to appoint a temporary senator. He or she would serve until a special election, to be held within 145 to 160 days.

On Monday, MoveOn started its petition drive to persuade Massachusetts Gov. Deval Patrick (D) to pick Frank. So far the group has collected about 5,000 signatures.

On Wednesday, the PCCC launched a website, www.appointbarneyfrank.com, promoting its own petition. The organization is also mobilizing its 25,000 members in Massachusetts with an email announcing the petition.

Both groups offer Frank's staunch defense of Social Security, Medicare and Medicaid as the main reason for their support. The PCCC email includes a quote, citing threats to those so-called entitlement programs, from Cynthia Curtis, a former Scott Brown voter who volunteered for his challenger, Sen. Elizabeth Warren (D-Mass.).

"As Elizabeth Warren takes a principled stand against cuts to Social Security, Medicare, and Medicaid benefits, we can't afford to have our other senator be lukewarm, undecided, or uncertain," Curtis writes. "We need someone who we are 100% confident will fight right alongside her. Barney Frank is that person."

As for MoveOn, Communications Director Nick Berning noted to HuffPost that its members "have been clear that protecting Social Security from any benefit cuts is a top priority."

Frank, who announced his desire for the temporary seat on MSNBC's "Morning Joe," told Politico that he is "well-qualified" to handle the upcoming fight over spending cuts. "I do think, immodestly, that given the important decision that will be made about these complicated questions in February, March and April, I'm very well-qualified because I don't know of anybody else who's been doing these things so continuously who's ready to jump in," he said.

John Kelley, a former telecommunications executive and MoveOn member who began the pro-Frank petition, told HuffPost that it was Frank's experience that earned his support.

"I admire him greatly," Kelley said. "I think he's done a heck of a job in his career. I paid into the Social Security system for 45 years. Now it's being jeopardized by Republicans. A guy like Barney Frank can advocate for us."

Also on HuffPost:

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