Wow, that's one hot discussion here. One could think you're voting for the next God for the next 2000 years.
Lemme reassure you: You're not.
You're merely voting for a president. If he fucks up, you have the next chance to correct your decision in two years, by voting republicans into congress. That's one of the many great things about democracy: It's rather tolerant towards errors because decisions can be revised.
And: Whether Western civilization in general and American in particular will fall is way beyond every president's power. At least that's what i think and very much hope.