Are you asking "legally?" or do you mean "force?"
I was referring to a “legal” action.
The political process would have to be exhusted before this could be tried. And, that includes impeachment and conviction and/or the finding of the SCOTUS that the POTUS is unfit to be in office and that removal is the only way to safeguard the country. Also, if a crisis (IE a terrorist attack or a missile launch) threatens the US in a major way (Survival of the US or threat to large numbers of civilans) and the POTUS either tries to allow the crisis to happen or helps out the adversary, and there is no time for the political process to intervene, a case for temporary removal can be made.