system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What safeguards prevent a corrupt President from taking control of the United States?

I was talking to a friend recently, who claimed that, any day he wanted, the President of the USA could enact martial law and turn the USA into a dictatorship. I know this is extremely far-fetched, but I can't find what actual safeguards exist to prevent this type of scenario.

Exactly how much power does the President have, and how difficult would it be for him to impose an authoritarian government? Alternately, how difficult would it be for the President and a group of corrupt officials, working together, to impose such a government? Is this, in any way, a realistic fear?
gpt
There is a common belief that the President holds a LOT of power.  Everyone wants to complain about how much trouble we are going to be in if "insert name here" is elected President, or even put all the blame on them when they are in office and out.  This simply isn't true.

The President does have power, some of which he can enact without immediate question such as declaring war.  However, the other branches of the government can question it afterwards and even overturn his rulings.  

I believe the President can enact certain policies that would temporarily give him extra power but never to such an extreme extent.

Too many people are fearing one man.  Politics are all about swaying people's perception of our leaders to get people to go along with decisions we won't normally want.  Republicans are well known for this, or in many people not known but should be.

I find it even more disturbing how when President G.W. Bush was in office if anyone even spoke a negative word about him people would say "You are not patriotic if you can't support your President!".  This prevented many people from bashing what is arguably one of our worst Presidents.

Turn to today and you hear people saying "Obama is worse than Hitler!", yet no one even bats an eye.  Maybe people should be more afraid of what is turning into a witch hunt to oust Obama and put in a Party which is willing to twist any situation to give "them" and not us an advantage.

Sorry for turning it into a political message, just frustrated with politics today.

TL;DR: There are 3 branches of government, the president is only one of them.  They check and balance each other.  You only have to worry about what happens when all 3 decide to do horrible things.

EDIT:  This has sparked tons of comments so just to be clear.  The President can not declare war but he can however move the military into a foreign country and take military action.  This is not the same as declaring war but is still a very hostile action without permission from congress.