Story highlights More than 300 former Obama campaign staffers signed a letter urging Elizabeth Warren to run

The letter includes low-level organizers and major tech and data staffers

Warren continued her rise on the national stage as she took center stage in this week's spending fight

More than 300 former Obama campaign staffers signed an open letter Friday morning urging Massachusetts Sen. Elizabeth Warren to run for president in 2016.

The letter draws parallels between Obama's come-from-behind insurgent candidacy and Warren, who would enter the race an underdog against former Secretary of State Hillary Clinton if the latter runs, as expected.

Clinton is seen as the likely Democratic nominee if she jumps in the race, and leads every survey of the potential Democratic field by double digits. But the same was true during her first run for president, in 2008, when a then little-known senator from Illinois jumped in and upended what many expected to be a coronation for the former first lady.

"We believed in an unlikely candidate who no one thought had a chance," the letter opens.

"We know that the improbable is far from impossible," it goes on.

The letter declares that "rising income inequality is the challenge of our times, and we want someone who will stand up for working families and take on the Wall Street banks and special interests that took down our economy."

It's signed by both low-level field staffers and researchers and a handful of more prominent Obama alums, including Rajeev Chopra, who served as chief information officer for both of Obama's presidential campaigns; Judith Freeman, who was new media field manager on the 2008 campaign; and Catherine Bracy, who directed the tech field office for Obama's reelection fight in San Francisco.

Most of the more prominent alumni of Obama's presidential campaigns have already signed onto the campaign infrastructure that's building around a likely Clinton run.

Jim Messina, Obama's 2012 campaign manager, has joined the pro-Clinton super PAC Priorities USA as a co-chairman, and White House advisor John Podesta is expected to leave his post soon and is considered a top pick for Clinton campaign manager.

The grassroots organizing group geared towards a Clinton run, Ready for Hillary, has signed on 270 Strategies, the firm launched by top Obama campaign aides Mitch Stewart and Jeremy Bird.

Progressives remain wary of a Clinton candidacy, however, and have been urging Warren to run for months. She has repeatedly denied any interest in a bid, and says she has no plans to jump in the race.

But progressives aren't waiting for her to make the decision — they're taking steps to encourage her into the race in hopes she'll change her mind. Just this week, a major national progressive group, MoveOn, announced a million-dollar effort to draft Warren into the race.

The draft efforts are building as Warren continued her ascendance on the national stage this week as a central figure in the government spending fight.

She led progressive opposition to a government funding bill, sparked by unrelated policy riders rolling back a key plank of the Dodd-Frank financial reform bill and raising caps on donations to parties, and ultimately drove enough Democratic opposition that the funding fight came down to the wire Thursday night.

The development was an early, but clear, indication that the progressive wing of the Democratic Party is angling to have more influence on activities on Capitol Hill through 2016 and beyond.