Cicero

"A nation can survive its fools, and even the ambitious. But it cannot
survive treason from within. An enemy at the gates is less formidable,
for he is known and he carries his banners openly. But the traitor
moves among those within the gate freely, his sly whispers rustling
through all the alleys, heard in the very halls of government itself.
For the traitor appears not traitor, he speaks in the accents familiar
to his victims, and he wears their face and their garments, and he
appeals to the baseness that lies deep in the hearts of all men. He
rots the soul of a nation, he works secretly and unknown in the night
to undermine the pillars of a city, he infects the body politic so
that it can no longer resist. A murderer is less to be feared."
- Cicero, 42 B.C.