Mayor McDonough, the mayor of Diamond City, expelled all of the ghouls and synths (except Valentine) from Diamond City.
However, we know that from his
brother's comments as a companion, Mayor McDonough appeared "different" when he expelled the ghouls and synths. The wikia article states that it is unknown when he was replaced by the synth.
Was Mayor McDonough already
a synth in the service of the Institute
by the time he issued the banishing edict?
Best Answer
Yes - this was part of Mayor McDonough's election campaign, during which he capitalized on the citizens of Diamond City's fear over synths and ghouls to gain popularity and ultimately get elected. Once he was finally elected he followed through on his promise and had all ghouls and synths expelled from the city.
It is entirely unknown and not mentioned anywhere within the game literature or in game content when the real Mayor McDonough was replaced by the synth M7-62.