He made the same mistakes many have made in American politics - taking for granted that the others around you love this country and want what's best for her people. He must've realized at some point that not only do most DC people not care about this country, they actually despise it and us, and only seek their own enrichment from gaming the system. And no doubt literally everyone he encountered lied to him in dozens of ways, and took advantage of his care and concern. If Evil cannot convert you to its side, it will always use your own goodness against you.