The prospect of turning Washington, D.C., into the 51st state has opponents on the offensive.

The U.S. House of Representatives passed the D.C. statehood bill known as H.R. 51 in April along party lines, with Democratic proponents saying the city’s residents deserve full self-rule and representation in Congress. The Senate, control of which is split 50-50 between the parties, hasn’t voted on its companion bill, S. 51.

Objections to the measure range from claims the District of Columbia is too small for statehood; to charges that adding two U.S. senators in an area that traditionally votes for Democrats represents a partisan power grab; to observations that the seat of federal government is located outside state boundaries for a reason—to protect it from interference.

As far as the Constitution is concerned, any area can become a state as long as two conditions are met: Congress must approve the request, and if the new state will be carved from one that already exists, that state must give its consent.

“That’s happened a lot,” said Steve Vladeck, a law professor at the University of Texas who is an expert in constitutional law. “Vermont was part of New York. Maine was part of Massachusetts. Kentucky was part of Virginia.”