If you think 2017 was bad, imagine an America without allies fighting another two-front war, this one involving nuclear weapons, under the leadership of the most hated president in modern history, while a torture apologist runs the C.I.A. The world right now is a powder keg. Trump, an untethered maniac, sits atop it, flicking a lighter that Republicans in Congress could take away, but won’t. If everything goes up in flames, we can’t say we weren’t warned.