Lancer, this is interesting can you actually support two teams from roughly the same area? Football (soccer) is so tribal in England.
Baseball can be, too, but I think we move around a lot more than the Brits might. Also, The Orioles and the Nationals are in different leagues, the O's are in the American League, and the Nationals are in the National League (just a coincidence about the names).
DC and Baltimore both have their own football teams, too, but there are so many people in the area from Baltimore and the head of the Chesapeake Bay, down through Washington and into NE Virginia, that they can support all the franchises.
Hard to say which area supports which teams and sports better. DC had a baseball team, back in the day, the Senators. In 1960, they moved to Minnesota to become the Twins, and Washington was awarded a new franchise in an expansion. But that franchise chose to move to Texas after the 1971, becoming the Texas Rangers. It was only when the Montreal Expos were close to folding, that MLB sanctioned returning a franchise to the national capital. On the other hand, Baltimore picked up its baseball team from St Loius, where they were the St Louis Browns, but they lost their original football club, the Colts, who moved to Indianapolis. But Baltimore was later awarded a new franchise in an expansion, the Ravens.
At one time, New York City hosted 3 baseball teams (The Yankees, the Giants and the Dodgers), and St Louis, Philadelphia and Boston each had 2 (the Cardinals and the Browns, the Athletics and the Phillies, and the Red Sox and the Braves, respectively).
Prost!
Brad