"Within the Democratic Party, you're talking about a lot of constituencies that can propel a campaign," said Doug Thornell, managing director at SKDKnickerbocker and a former advisor to Van Hollen and Rep. Elijah Cummings, who is considering running.
Adding a surprise Senate retirement to that dynamic has the potential to create a stampede. Most of the candidates thinking about running have a powerful cohort urging them forward.
"It's personal for us," said EMILY's List spokeswoman Marcy Stech. "Senator Mikulski was our first woman we ever helped get elected back in 1985. For EMILY's List it's very important to carry on her legacy with another Democratic woman." The group already has spoken with multiple prospective candidates and is expected to be one of the biggest outside spenders in next year's primary.
"Given than Montgomery County is now a majority culturally diverse county, it would be nice to have a representative of color," said Laurie-Anne Sayles, president of the Montgomery County African-American Democratic Club.
African-Americans make up a larger share of Maryland's population than any state outside the South. Yet Maryland Democrats have nominated only one black candidate for statewide office: losing 2014 gubernatorial candidate Anthony Brown, the former lieutenant governor. In the state's last open Senate race in 2006, Kweisi Mfume, a black candidate, lost a racially polarized Democratic primary to current Sen. Ben Cardin.
That campaign "revealed that there are still some racial divisions even within the Democratic Party in the state," said St. Mary's College political science professor Todd Eberly. "I think that for a lot of African-Americans, there's sort of a sense that their votes are absolutely relied on, but their candidates are frequently passed over."
Meanwhile, MoveOn.org and the Progressive Change Campaign Committee point to the relatively safe Democratic seat as one of the statewide races they can impact next year. The PCCC endorsed Edwards immediately.
"Seats like this don't come open very often, so this is an opportunity for progressives, and that's why it's important to take advantage of," said MoveOn spokesman Nick Berning. His group already has put out statements attacking Van Hollen, the first candidate to join the race, for once suggesting he was "willing to consider" increasing the Medicare eligibility age.
For his part, Van Hollen is taking early steps to avoid progressives' ire, making a point to clarify that he intends to "fight any efforts to raise the Medicare retirement age or make cuts to Social Security."
Maryland's three population hubs also are heavily invested in finding the next senator. Baltimore has typically dominated statewide offices and been the political center of the state. But its population and influence has declined, and Van Hollen and Edwards are from growing Montgomery and Prince George's counties, respectively, where local elected officials rushed to endorse them in the past week.