The District of Columbia is not a state. Therefore, it cannot have citizens - only temporary residents. Those temporary residents are citizens of the state in which they resided prior to coming to the District of Columbia. Therefore, they should vote in those states - by absentee ballot if necessary.
Not to worry - zero swore he'd preserve, protect, and defend the Constitution of the United States. He'll veto it, I'm sure. /S
“The House of Representatives shall be composed of Members chosen every second Year by the People of the several States, and the Electors in each State shall have the Qualifications requisite for Electors of the most numerous Branch of the State Legislature.
“No Person shall be a Representative who shall not have attained to the Age of twenty five Years, and been seven Years a Citizen of the United States, and who shall not, when elected, be an Inhabitant of that State in which he shall be chosen.”
14th Amendment:
“Representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State ....”
Is it really that hard to understand?