What’s his source for this exchange between FDR and Hoover?
No sources at all, that I can find.
So much for Coleman.
Both Prange and Victor discuss Dusko Popov, code name Tricycle, and his meeting with J. Edgar Hoover.
Prange does not, but Victor does claim that Hoover reported Popov's interest in Pearl Harbor to President Roosevelt.
But even Victor (c2007) does not purport to quote from a conversation where FDR dismissed Hoover's warning.
We should note that Hoover had long been wire-tapping the Japanese consulate in Hawaii, and well knew of their interest in the US fleet, and would doubtless have reported it to President Roosevelt.
This is explained away as being nothing more that "routine" espionage, of the kind every nation did on all others.
But Popov's interest in Pearl Harbor was of a different nature, and should have excited more interest at top levels of the US government than it did, imho.
My copy of Coleman's book is a Kindle PC version, and I had not noticed before that he apparently included no references to source material.
WTF?
So, until I can learn something new about it, I'm inclined now to just cross Coleman off as nothing more than a toxic collection of rumor and innuendo...