CORRECTION: Earlier versions of this story said Rep. Donna F. Edwards (D-Md.) narrowly defeated incumbent Albert R. Wynn in the 2008 Democratic primary. In fact, Edwards beat Wynn by a wide margin. This article has been corrected.

Rep. Donna F. Edwards (D-Md.) announced her candidacy for the U.S. Senate Tuesday morning with a video message to supporters that emphasized her years of political activism in Prince George's County and her work  advocating for women’s rights.

Edwards, 56, is vying to replace Sen. Barbara Mikulski (D), the longest-serving woman in Congress, who announced last week that she would retire in 2016. Edwards will face fierce competition for the Democratic nomination from Rep. Chris Van Hollen, who launched his campaign last week and has the support of Senate Minority Leader Harry M. Reid (D-Nev.). Other Maryland Democrats -- and several Republicans -- are contemplating the race as well.

If she wins the nomination, and the general election in November, Edwards would become the fifth African American and the first black Marylander elected to the Senate — a fact that is not lost on her national network of followers.  Her candidacy has drawn early support from prominent progressive groups, many of which have supported her since she ousted a pro-business Democratic incumbent in a hard-fought congressional primary in 2008.

In her video message, Edwards -- whose district includes Prince George's County and parts of Anne Arundel -- laid out her record of investing in historically black colleges, protecting women's reproductive rights and beating back attempts to change Social Security and Medicare.

"No ifs, ands, buts or 'willing to considers,'" Edwards said in a jab to Van Hollen, who calls himself a "pragmatic progressive" but has been criticized by progressive groups for his willingness to compromise in order to forge budget agreements in Congress.

Before coming to Congress, Edwards  spent years as a public-interest lawyer and nonprofit executive. She co-founded and led the National Network to end Domestic Violence -- a group that helped push the Violence Against Women Act in 1994. The legislation she has sponsored in Congress includes bills addressing access to childcare, fair wages and equal pay for women in the workforce.

In her message, Edwards recalls working with a group of residents years ago who opposed construction of the National Harbor development on the banks of the Potomac River, and winning several key concessions from the developers.  Her story echoes Mikulski's own political narrative, which began when she organized communities in Baltimore City against the building of a highway through their neighborhood.

While Montgomery County Democrats are coalescing behind Van Hollen's Senate bid, Edwards may have a harder time winning the support of the Prince George's County political establishment.

She took office in 2009 as a complete outsider after a primary victory over then-Rep. Albert Wynn, a respected black Democrat who helped launched the careers of many county officials.

Although she has developed key relationships since then with a few local politicians -- such as former Lt. Gov. Anthony Brown, who quickly endorsed her -- Edwards is not as popular among her colleagues in Prince George's as she is nationally. Her reputation for contesting the local leadership's positions on issues like gambling has alienated her from many state and county lawmakers.

Running for Senate means Edwards must give up her congressional seat in 2016, and there are many Democrats in the county thinking about whether to run to replace her. Names being circulated include state Sen. C. Anthony Muse, whose state district overlaps with Edwards's congressional district, and who ran unsuccessfully against Sen. Ben Cardin in the 2012 Democratic primary; former state’s attorney Glenn Ivey, who dropped out of a bid to challenge Edwards in 2012; council members Andrea Harrison and Derrick Leon Davis; and state Del. Michael Vaughn.

Brown, who lost the 2014 gubernatorial race to Republican Larry Hogan and ended the campaign in debt, has been making calls to gauge enthusiasm for his own possible run, several Maryland Democrats said.