The only mechanism to do so would be impeachment, which would (given the current makeup of Congress) require a bipartisan majority vote in both the House and Senate. Needless to say, the Republicans would not do so lightly and the evidence would have to be very strong. On the other hand, a high level of suspicion may be enough for Congress to block Trump's actions on things like weakening NATO, cutting U.S. intelligence agencies, or lifting sanctions on Russia.

The other question is whether the GOP is now so cynical, corrupt and partisan that it would shrug at the idea of a Manchurian candidate occupying the Oval Office as long as he's nominally one of theirs.