“If the US president started a fistfight, what would the Secret Service do?
As in, in public, the president threw the first punch at a citizen, and a fight ensued.”

Assuming that the presidential press pool is there (as it should be; they follow the President wherever he goes when he leaves the White House), and it is clear that it is the POTUS who threw the first punch in a situation where self-defense is not an issue, the Secret Service will jump in and separate the POTUS, dragging him away exactly as they would if he'd been the one attacked. Another part of the Secret Service detail would detain the victim (violently, if he was belligerent prior to the incident and/or if he punched back), and take him into custody, passing him on to local or federal authorities for possible prosecution.

IF the victim fought back, there might be charges pressed for assault, particularly if he was belligerent prior to the attack (i.e. running off his mouth in order to incite a fight with the POTUS). If the attack was 'unprovoked', chances are that there will be no charges, or maybe misdemeanor charges based on the victim's actions during the ensuing fight.

However, IF the victim did NOT fight back, he will be released after a basic investigation (maybe charged with public disturbance if he 'provoked' the attack... in which case he'll be held longer), and he can press charges of assault against the POTUS, along with filing what will be a media circus of a civil lawsuit.

Regardless of how it happened, the POTUS will have to get himself a lawyer. Local authorities will assume jurisdiction over the fistfight, and through the POTUS's lawyer, make arrangements to interview the POTUS.

The POTUS will never be paraded in handcuffs; everything will take place through his lawyers.

Chances are very good that IF the case ever sees the light of day, the POTUS will eventually plead to misdemeanor assault - "eventually" being the operative word - and may even face impeachment in congress, particularly if congress is hostile (i.e. controlled by the "other" party).

Whatever happens, the media on both sides of the aisle will be very happy.

Source: https://www.quora.com/If-the-US-pres...ret-Service-do

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