Currently, there are impeachment investigations going on for the POTUS. Lets say the POTUS is formally impeached and Trump is removed from office. However Trump refuses to leave the White House on claims that the "witch hunt" impeachment is false and not legally valid. Is it possible to remove the President from the White House by force?
If the Senate has convicted by the necessary majority, Trump would no longer be the President - Mike Pence would be. There is no legal difficulty in removing ordinary citizens from the White House.
Of course, President Pence might decide that he didn't mind ex-President Trump remaining in the White House, and I think the law enforcement agencies would be obliged to respect that.