Politically, the DC area is extremely left-leaning. The District of Columbia is one of the most reliably Democratic jurisdictions in the country; since it has been allowed to vote for President in 1960 (DC has a very odd political status), the smallest margin of victory for a Democratic presidential candidate was 57% in 1972. The margin this year was 87% (Hillary got 91% of the vote, while Trump got 4%). Even outside the District, in the Maryland and Virginia suburbs, the area is very liberal, especially on the Maryland side. As someone who's not a native, it's almost a bit disorienting how monolithic political opinion is here; you can certainly find people who are politically conservative, but you might feel like you have to seek them out. This might change a bit when there is a conservative President (I wasn't here the last time that was true), but I don't think it does very much; most federal employees are not directly appointed by the President, and most federal employees are leftists.
Culturally, the area is also quite liberal. The DC area has one of the largest LGBT populations in the country. There is also a strong history of minority activism. DC decriminalized the possession of marijuana in 2015, although it's not normalized enough that you should be smoking outside of a private residence (and there's also the risk that it could be invalidated at any time by the federal Congress - again, DC has a very odd political status!). On the flip side, to me, again as a non-native, it seems very formal and buttoned-down. Even the hipsters wear nice shirts. People tend to be more reserved than they are in much of the rest of the country, perhaps in part because the area tends to be transient.