This is where I'm going to get super spicy, but the War Department had far more to do with the failure of the Peninsular campaign than Mac. Richmond falls in 1862 if Mac gets to route his logistics up the James river, instead of the War Department forcing him to route them up the York river.
The only reason the seven days battle is even possible in the first place is because Mac is forced to split his army across the swollen Chickahominy river, something that isn't necessary if he is routing his logistics up the James.
Why did the war department force him to do it that way
They were paranoid about the ANV moving north (despite also heavily manning the Washington defenses) so they wanted to force the AOP to maintain a presence north of the Chickahominy to theoretically prevent any refusal by Mac to move north to follow Lee.
The usual idiotic Halleck-Lincoln political games.
Why did that man keep his job
Frankly, I think people just don't get that the ACW was a complete amateur hour affair from start to finish, lead by people who never expected to lead anything larger than what would be considered a small to medium sized corps.
Anglos are terrible at professional warfare send tweet
People constantly talk up the Union's manpower and industrial advantage, but by far the biggest bottleneck during the war was semi-competent officers. The ANV lucked out immensely at the start by somehow ending up with three officers semi-capable of leading large forces.
If you factor in died of wounds, it's likely that more Americans died in combat on a single day at Antietam than during the entirety of the Revolutionary War.
Spicy ass take: this is a classic case of an imperial occupation and counterinsurgency army being totally unprepared for a peer or near peer cony
Extremely so.
Biiiiingo