Which has nothing to do with your request for citations about the presidents powers. The powers are what they are whether you think they are right or wrong doesn't change the reality of those powers.
Also to start war does not mean a declaration of war has to be made. The aggressor rarely formally makes a declaration of war.
That whole "declaration of war" thing was very much an 18th century concept. Sure, it lingered, and it serves some purpose yet today, if only someone would actually exercise it. However, the modern world doesn't work the same way the world worked at the founding of the republic.
It's unfortunate that, these days, it's kind of uncertain exactly who has the power to do what. You end up with resolutions that "authorize the President to use force if necessary" and similar wording, which allows congresscritters to vote for things which sort of mean one thing and sort of mean another, and gives the President really broad powers.
When it comes to Trump, the President certainly has power to order military action with very little, and in some cases no, Congressional consent. Because of his self-centeredness and lack of impulse control, it's not a power I want Trump to have. However, to the point of this thread, even then I doubt he would destroy the country or the world. It's a theoretical possibility, but not something that keeps me up at night.
Meanwhile, I think the apocalyptic visions of what will happen if Clinton wins are, as others have alluded to, the consequence of years of just plain hate being spewed by right wing radio and other media. The people who limit themselves to those sources of media end up with a bizarre, skewed, view of the world.