Former Attorney General Eric Holder Eric Himpton HolderThe Hill's Campaign Report: Trump's rally risk | Biden ramps up legal team | Biden hits Trump over climate policy Biden campaign forming 'special litigation' team ahead of possible voting battle Pompeo, Engel poised for battle in contempt proceedings MORE on Thursday endorsed House Minority Leader Nancy Pelosi Nancy PelosiHoyer: House should vote on COVID-19 aid — with or without a bipartisan deal Ruth Bader Ginsburg lies in repose at Supreme Court McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE (D-Calif.) for Speaker, calling her "an architect of the recent midterm success."

Holder, a possible 2020 contender, argued on Twitter that Pelosi has been "a target of the right wing" because she is "successful" at leading the Democratic party.

"Nancy Pelosi has been an effective national leader, an architect of the recent midterm success and a great partner in the fight against gerrymandering," Holder tweeted. "She’s been successful-that’s why she’s a target of the right wing. She should be the next Speaker of the House."

Nancy Pelosi has been an effective national leader, an architect of the recent midterm success and a great partner in the fight against gerrymandering. She’s been successful-that’s why she’s a target of the right wing. She should be the next Speaker of the House. — Eric Holder (@EricHolder) November 15, 2018

The endorsement from the former top Obama administration official comes as a number of Democrats have signed onto a letter pledging to vote "no" on Pelosi for Speaker.

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The letter so far includes the signatures of around a dozen incumbent Democrats and six incoming Democratic lawmakers, according to The Huffington Post.

Pelosi is facing opposition from an incoming freshman who campaigned on opposing her leadership, as well some incumbents, who say the party needs a fresh face at its helm. The group of insurgents has not yet put forth an alternative to Pelosi, who has led the Democratic Party in the House since 2003.

Pelosi in recent weeks has launched an expansive lobbying campaign within her caucus, urging her allies to release statements in support of her bid to win back the Speaker's gavel when Democrats take over control of the House in January.

The campaign has so far found success, with multiple previously critical Democrats going public with their support for the California Democrat.

Pelosi has sought to appease some of her critics by saying her run as Speaker would be "transitional," but she has not specified a time frame.