Theoretically all one needs to do is control Congress and a single state, the above DC example could just be used with Massachusetts for example. The above Republican method would be pretty tricky because dividing 25 Republican controlled into 3 states that would all still vote Republican is much easier said than done...it'd work with like Wyoming but not Ohio for instance.
If you're setting aside all notions of reasonability whatsoever for a power-grab like this in the first place, there's no problem splitting any Republican State into 3 Republican states. Ohio for instance: Just split off Mercer and Adams counties, call them West Ohio and South Ohio, and you're done.
