Hoover survived for a long time as FBI Director. He must have had the goods on a lot of officials and politicians, as well as making himself useful to them.

https://en.wikipedia.org/wiki/J._Edgar_Hoover#Sexuality

"Later in life and after his death, Hoover became a controversial figure as evidence of his secretive abuses of power began to surface. He was found to have exceeded the jurisdiction of the FBI,[1] and to have used the FBI to harass political dissenters and activists, to amass secret files on political leaders,[2] and to collect evidence using illegal methods.[3] Hoover consequently amassed a great deal of power and was in a position to intimidate and threaten sitting presidents.[4]"