Can we add a state with a simple majority vote in the Senate? I thought it took two/thirds.
Also, adding DC takes a Constitutional amendment - I think the dems recognize this.
Nope. Simple majority. Article IV, Section. 3. "New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress."
If the Dems recognize that you can’t add DC without a Constitutional amendment, you need to talk to the Dems. The House just passed a bill giving DC statehood, and almost all the Democrats in the Senate have indicated that they would pass such a bill. In addition, the Dems could pack the courts, including the Supreme Court, if they get rid of the filibuster.