The Orioles claim that if a team is put in Washington D.C. or Northern Virginia it will draw as much a 35% of the fan base from Baltimore. Critics say it is not any where close to that.
I think a little competition would be good for the area. It would force the O's to field a more competitive team so they would keep up the fan base and Washington would be the same way. There are enough people to support two teams and people could watch games in both cities so they can see American and National league baseball more than just Interleague play.