It would have no impact on the Electoral College, but would add two Senators.
It’s another issue Republicans should have addressed years ago. The only logical solution is to reduce the District to the Federal Triangle, return the rest to Maryland, and repeal the 23rd Amendment. Maryland probably gains a safe Democrat House seat, but the Democrats lose 2 or 3 electoral votes (depending on how the House is reapportioned) and we remove the threat of 2 permanent Democrat senators.
Congress might be able to do this without Maryland’s consent. Repealing the 23rd Amendment probably would not be controversial, because otherwise the District’s 3 electoral votes would either be controlled by the President and his family as the only remaining residents of the District, or by Congress utilizing its power to direct the manner of appointing the District’s electors under the 23rd Amendment.