There’s probably not much he could do. The Electoral College is a state thing. BUT, he could talk to the hold-out states in the National Popular Vote Interstate Compact (NPVIC) and try to encourage them to join?
If Texas, Florida, and Ohio were to join the NPVIC, they would bring the total to 296 electoral votes, surpassing the 270 needed to make the compact effective.
Done.
Other combinations of other states would work too. And it takes effect automagically.
@amarand @MotherDucker Not exactly automatically. There would be a court battle leading to the SCOTUS, and we all know what they would rule.