I think they would pick someone with similar body type and the right height then go from there with coaching to get major body movements right, the way they did with the Hillary doubles and for others. You'd need someone with very good mimicry skills to start with. A few days ago there was a clip of Biden* going up on a stage to speak, wearing a hat, sunglasses AND a face mask for a public appearance. Obviously you can't do CGI for a crowd of people who aren't in on the joke.