Chain of Command

The U.S. usually won wars and battles because we had chain of command because we are an egalitarian country where anyone literally can rise to be President or General unlike many countries around the turn of the 1800s to 1900s, though now most countries have followed our lead because "Chain of Command" actually works in all situations. However, it is a new (only one century old idea) for most countries at this point.

So, if anything happens to the President and Vice president the Speaker of the House becomes President of the United States.

So, from this point of view he is 2nd in command of the nation. That's why this position is so very important "chain of command" wise and why it is so very important to have a "moderate" who all the people can somewhat support be in this position and not be "just stolen" by either Conservatives or Liberals and someone who can represent "All" the citizens of the U.S. AND NOT JUST ANY EXTREMIST POINT OF VIEW.