He's no dummy. He was a US Attorney in NY before, and was also in the Bush admin where he knew how to thwart Gonsalves skullduggery at Ashcropt's hospital bed. That was heroic. He knew how to handle bad actors then.
He was the fu_king director. He had the power over the plotters/Giuliani and should have know how to use it.
What, he forgot how to act when took the Director's job? He got fooled by fake reports to him? He of all people should've known of the Hatch Act and not to get involved in an election that close to its finale.
IMO he was no weak figurehead at the mercy of connivers in his agency. He could have put on the brakes to the whole deal agency-wide with threats of dismissals.
He didn't. He sent that letter and got trump elected because, IMO, he was more loyal to his party than the electoral process and the country. He himself went "cowboy" just as he did in the summer without the AG's knowledge when he publicly chastised Hillary instead of just absolving her in the fake email scandal.
He tried to make up for it later once he realized the monster trump is with his investigation but was turned on by the bastard he helped get in office hoisted on his own petard.
It's Shakespearean, no doubt, and tragic, but he contributed to his own downfall. He has to live with what his letter wrought, and unfortunately, so do the rest of us.