Rep. Donna EdwardsDonna F. EdwardsThe Hill's Morning Report - Presented by Facebook - Dems, GOP dig in on police reform ahead of House vote The Memo: Strife turns up heat on Trump Democratic Senate candidate blasts own party for racial 'foghorn' MORE (D-Md) announced Tuesday she’ll run for the open Maryland Senate seat in 2016 to replace retiring Sen. Barbara Mikulski (D-Md.).

Her entrance sets up a primary battle with Rep. Chris Van HollenChristopher (Chris) Van HollenDozens of Democrats call for spending bill to pass 'climate test' GOP tries to take filibuster pressure off Manchin, Sinema Overnight Energy & Environment — Biden set to restore national monuments rolled back by Trump MORE (D-Md.) and potentially several others.

“I’ve lived the American dream, the Middle-Class American dream, the one you have to work hard for just to hold on to, the one that’s slipping away for far too many families,” Edwards said in a two-minute YouTube video announcing her candidacy.

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“These are the people I fight for,” she continued. “The corporate special interests are going to come after me with all their money. But if you come with me on this fight, there’s no way we can’t win. And when I step into Barbara Mikulski’s shoes as your next senator, you’ll always know where I stand. With you.”

Edwards is a favorite among progressives, who helped her knock off a long-time Democrat in a primary in 2008. Last week, two of those groups, Democracy For America and the Progressive Change Campaign Committee, launched efforts to draft her to run for the open Senate seat in 2016.

Edwards’s candidacy sets up an intriguing and potentially bitter primary fight with Van Hollen, who announced his candidacy last week.

While Edwards will be the grassroots liberal favorite for the open seat, Van Hollen appears to be the establishment favorite. Last week, Senate Minority Leader Harry Reid (D-Nev.) gave him an early endorsement, in what was a strong signal to the huge field of other Democrats potentially weighing bids.

Van Hollen, the ranking member on the Budget Committee and former chairman of the Democratic Congressional Campaign Committee, has long been eyeing the Senate and is well-positioned with $1.7 million in his campaign account.

But he could be facing consistent attacks from liberal groups, who question his commitment to defending entitlement programs.

Two groups, MoveOn.org and CREDO Action, responded to Van Hollen’s candidacy by pointing to comments he made during the contentious 2012 budget fight, when the Maryland Democrat appeared open to raising the Medicare eligibility age and making cuts to Social Security as part of a deal to avoid the looming fiscal cliff.

At the time, Van Hollen reportedly said he was “willing to consider” any options that would lead to an agreement, and in her YouTube video, Edwards took a swipe at the remarks.

“That’s why I ran for Congress, and it’s what I’ve done in Congress … standing up to anyone that would compromise away social security and Medicare,” she said. “No ifs, ands, buts or willing-to-considers.”

An aide for Van Hollen told The Hill last week that he will fight any efforts to raise the Medicare retirement age or make cuts to Social Security.

"From day one, Chris Van Hollen has fought for retirement security for all Americans,” the aide said. “He has authored four House Democratic budgets, and each explicitly protected Social Security and strengthened Medicare. During budget negotiations, he stood up to Republican efforts to dismantle the program and erode its benefits with the damaging chained CPI calculation. He helped lead the charge against President Bush's plan to privatize Social Security. And he will continue to fight any effort to cut benefits or raise the retirement age."

But the fight for the Democratic nomination for Maryland Senate might not be confined to Edwards and Van Hollen. There is still a huge field of potential contenders weighing bids, including four other House members, Reps. John Delaney, Dutch Ruppersberger, Elijah Cummings and John Sarbanes.

Former NAACP President Benjamin Jealous, former Maryland Lt. Gov. Kathleen Kennedy Townsend, a member of the powerful Kennedy family, have also both expressed interest in a bid.

And Baltimore Mayor Stephanie Rawlings-Blake, Labor Secretary Tom Perez and former Lt. Gov. Anthony Brown have all been mentioned as potentially interested in seeking the nomination.