Damn, I feel bad for him, but he should've seen it coming. In the political and social world, one must always have several plan Bs and Cs. "The best defense is a good offense" is somewhat true, but what if the offense fails? Then you'll be left vulnerable. He should've made backup plans for if his offense/blackmail didn't work.
Sure, adding more security would give the mastermind more room to add spies, but then not doing anything at all wouldn't be any better. His decision of not doing anything at all was one of the stupidest decisions I've seen in manga.
The enemies were masters of manipulation, and hadn't hesitated to kill someone after blackmailing them. He should've expected the worst. Those kinds of criminals have no morals, and would stoop as low as possible to fulfill their goals.
Anyways, end of rant. Other than that I found the MP too innocent and naive, I quite like this arc. Very interesting story and it's nice to see Augustus in action.