If Trump says "Im not leaving office." in January 2021, there is nothing they can do

I see so many democrats are still saying that Trump is bluffing. But I think he means it. If he refuses to leave office in Jan 2021 even after he lost, there is nothing they can do. Trump just have to move teh troops and the commander that are loyal to him to surround Washington DC and cover it up with tanks. Democrats will have a hard time cracking that shell.