I think they would do the right thing. Surround the Whitehouse and incinerate it.
“A hypothetical... If a president is impeached for being an unqualified fraud, and then during the trial he orders US military to arrest a few Congressmen who voted for it and to surround the capital building, do you think the military would either stand down or take him out?”
In that case the military would stand down because the order would be unlawful. Also, except under “martial law”, the U.S. military cannot act in that capacity. This “hypothetical” situation would (the arrests) more than likely be carried out by U.S. Marshalls, not the military. I don’t know what they would do.