Epstein was selling kompromat to Russia and others. But Russia would be bad enough. You don't have to be doing the gross stuff going on at his place to be a national security problem. He was selling influence ranging from minor personal indebtedness to the worst blackmail material. You don't have to be at the really icky end of that spectrum to have participated in degrading national security.
Over Gmail? For so long? Without triggering three-letter-agencies? Fat chance.
I also can't explain why Tulsi Gabbard is the DNI. Can you?