D.C. is a weird political entity. Set aside by congress as the seat of government it is not a state, has no Senators, has a non-voting Representative, has no governor, does have a mayor whose power is limited. Defense of the Capitol building is the responsibility of the Capitol Police, a federal force. DC has no National Guard, must request help from neighboring states. The ultimate person responsible for D.C defense is, you guessed it, Trump. Rumor has it that as the mob marched past the Trump Hotel it was guarded by a strong phalanx of D.C. police.