The first U.S. senator elected directly by voters was a Silver Spring attorney named Blair Lee, who won a special election in 1913, months after the 17th Amendment changed the way candidates were selected for the Senate.
Lee, it turns out, was also the last senator in Maryland to come from the Washington suburbs.
Baltimore's metro area has dominated statewide politics in Maryland for more than a century. But the 2016 race to succeed Sen. Barbara A. Mikulski comes after decades of demographic forces have shifted the political center away from the state's largest city and toward Montgomery and Prince George's counties.
Though the field of candidates remains uncertain — several Baltimore-based politicians might still jump in — the 2016 contest will give downstate politicians their best opportunity in decades to claim a top political prize.
"It's going to become the norm, rather than the exception," said Douglas F. Gansler, the former Maryland attorney general — who was something of a harbinger of the shift. In 2006, Gansler and Peter Franchot became the first candidates from Montgomery County to win a statewide election on their own — that is, not as lieutenant governor — in 87 years.
Two Democrats from the Washington region have entered the race for the seat held by Mikulski in an effort to lock up endorsements and donors early: Rep. Chris Van Hollen of Montgomery County and Rep. Donna F. Edwards of Prince George's County. Others, such as Rep. John Delaney of Montgomery County, are considering a run.
A half-dozen Baltimore-area candidates, including Reps. Elijah E. Cummings, John P. Sarbanes and C.A. Dutch Ruppersberger, as well as Baltimore Mayor Stephanie Rawlings-Blake, are circling each other as they also contemplate campaigns.
But it is the Washington-area politicians who have several built-in advantages.
The first and most obvious is the number of voters — and, particularly, Democratic voters. Population growth outside Washington has meant that Montgomery and Prince George's counties now account for more than one-third of all votes cast in a statewide Democratic primary.
Baltimore's population, which peaked in 1950 at 949,708, had fallen to 622,104 by 2014. The number of people living in the Washington suburbs, meanwhile, grew more than fivefold over that period, from 358,583 to more than 1.9 million.
"If you're fishing, you want to go where the fish are," said Don Norris, director of the School of Public Policy at the University of Maryland, Baltimore County. "The fish are in the Washington suburbs."
After votes, the Washington suburbs also have an abundance of the next most important thing in elections: money. Of the 50 ZIP codes in the United States from which residents have contributed the most to federal campaigns, three are in Maryland — all based in Montgomery County, according to the Center for Responsive Politics.
Another advantage: The cost of television ads in the Washington media market is far higher than in Baltimore. A Baltimore-based candidate would have to spend more money to introduce himself or herself to voters in the Washington suburbs than, say, a Montgomery County lawmaker would have to spend in Baltimore.
The shift in the state's center of political gravity, decades in the making, became apparent when a Democratic Prince George's County executive named Parris N. Glendening was elected governor in 1994.
Martin O'Malley, who was born in Rockville but raised in Baltimore politics, chose a Prince George's County lawmaker, Anthony G. Brown, as his running mate in 2006.
All three leading Democratic candidates for governor last year — Brown, Gansler and Heather R. Mizeur — hailed from the Washington suburbs. They were beaten by Larry Hogan, an Anne Arundel County Republican, in the general election.
"Political power tends to follow economic development," said Fred Mason, president of the state AFL-CIO. The Washington suburbs, he said, "have shown themselves to be adept at growing economically and politically."
The dynamic is less of a factor for Republicans, whose base remains in Western Maryland, Harford, Carroll and pockets of Baltimore and Anne Arundel counties.
"Our power is in the Baltimore area," said Maryland GOP chair Joe Cluster.
While downstate politicians have gained ground, they have yet to win a Senate seat in modern times. The closest was GOP Sen. Charles McC. Mathias, who served from 1969 to 1987. His former House district included portions of Montgomery County, but Mathias himself was based in Frederick.
Former Rep. Michael D. Barnes, who had deep roots in Montgomery County, ran unsuccessfully in the 1986 Democratic primary for Senate in 1986. He lost to a politician who remains closely associated with Baltimore: Mikulski.
Geographic politics have long been a factor — and a point of debate — in Maryland.
"It's good for any major part of the state to put forward a candidate, to the extent that candidate maybe comes with a greater degree of sensitivity to the issues that face that part of the state," said Sarbanes, whose father, Paul S. Sarbanes, represented Maryland in the Senate for 30 years.
But he added that geography ultimately doesn't matter, so long as whoever wins looks out for the interests of the state as a whole.
"I don't think, in the end, if the candidate's worth their salt, that it's highly consequential that the person elected senator be from one place or another."
Baltimore Sun researcher Paul McCardell contributed to this article.
The share of Democratic primary voters in Maryland who live in Baltimore City and Baltimore and Anne Arundel counties.
Maryland Policy & Politics
Source: Maryland State Board of Elections