Would you obey an illegal or unconstitutional order?

First, every service member has taken an oath to follow LAWFUL orders. We also have an obligation not to follow unlawful orders. Examples: Lawful-“Report aboard ship prior to the expiration of liberty. Liberty expires at 0100 local time”; Unlawful- “March those POWs ahead of the platoon to clear the minefield”. A service members reply should be “Sir, I believe you’ve issued an unlawful order (to march POWs thru a minefield) and I am obligated to not follow/obey this unlawful order”.
Second, in the question asked (deploy forces to quell civil disturbances/violent protests), this can be a lawful order as long as the Posse Comitatus Act (which limits the powers of the federal government in the use of federal military personnel to enforce domestic policies within the United States) is complied with. This act dates to 1878, updated in 1958 & 1981. Nation Guard units under state control can be used within their respective state to perform as above (quell civil disturbances/violent protests).
Third, IMHO, protecting federal property from riot/arson, where the local law enforcement has been withdrawn or ordered to not protect is probably a reasonable/lawful use of federal forces (lawful order as long as Posse Comitatus Act is complied with); stopping a ballot count because the results are disagreeable (IMHO) is probably an unlawful order.

NO!

Fortunately for me this only occurred twice in my career. No I did not obey, to my officer in charge it was illegal, immoral, and probably fattening and would carry out the order. One occasion we pounded fists on his desk at each other but I finally convinced the Admiral that what he wanted to do was illegal. He relented and allowed me to show him the law and Navy Regs. Eventually he shook my hand and we went on from there. An old axiom though is "Let your conscience be your guide but disobey at your peril" You had better be right

This question looks like a set up to bash Trump, but I am genuinely concerned about whether or not the US military of today has enough knowledge of the constitution and the doctrine of separation of powers to make a sensible and legal decision in such an instance. I know I am in “old guy“, but for me the answer is “No, I would not follow an illegal or unconstitutional order!” I would hope that at least some of our senior leader ship (and I don’t have much confidence, based on what I’ve seen of late, that very many are of like mind) would feel the same way.

1st, we HAD an illegitimate sitting"POTUS", a man not o ly not natural born, as per the Constitution, but not even an US citizen, & all efforts to oppose him & his unlawful orders & acts were treated as CRIMES, indtead of being properly investigated, & evidence heard, which tells me those asking this question, now, do not WANT the truth here; the way it's worded says they want the narrative. Well, I can't & won't give it to them. We now have a 2nd illegitimate régime in place: a senile old man incapable of rationally dicarging the duties, & a NON- citizen (per the correct reading of the 14th A on citizenship) masquerading as VPOTUS. Obeying them is to betray the very Constitution to which we now sed to take our oaths, not to mention disobeying the higher laws of Yhwh God! These are people following & pushing the anti-Constitutional, anti- God, Satanic agenda, whom I cannot, in good conscience, obey under any circumstances. As an officer, the UCMJ required me to not follow such orders, had I been given such. As a citizen & Christian I must obey God's law when there is a conflict, & where the Bible isn't entirely clear on a specific issue, for example the jabs called "vaccines" erroneously, I revert to my professional training & experience & the Holy Spirit's guidance. The bottom line is no, Icould & would not obey unlawful orders, however, I would discern which "side" was telling the truth!

I thought this issue was fully answered at Nuernberg in 1945-46.

Sit back and watch.

In the present case,we know this person has flawed view of what has happened. I would not follow him at any cost. Those that choose to do so are entitled to their opinions. Being a sore loser, just shows how much he wanted to follow in Hitlers steps. We have never had a dictator and most agree, never will. Our constitution guarantees that freedom is for all not just the rich.

"... I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same ..." 1965, no expiration date.
For those currently serving it applies most specifically.
To obey an unconstitutional order would violate my oath; to obey an illegal order would violate my moral code.

The only reason I can see someone asking this question in the current times is to stir the pot and cause a mess. As a “civilian supporter” it really isn’t your position to ask any military personnel Retired or Active duty whether or not they would obey a “legal or unconstitutional order” unless you are trying to do so. In my honest opinion. Who are you really working for and what’s your motivation behind this question?