Could a leader similar to Hitler obtain and hold power in the United States today?
No, such a leader could not come to power in the United States today. There are two reasons for this.
First, such leaders only come to power when people are extremely angry and desperate. While Americans are getting angrier at their government, they are not yet desperate. American life is still generally too good for us to put our support behind a dictator.
Second, such leaders get and hold power in places that do not have a firm commitment to democracy. Germany in the 1930s had never truly been democratic. By contrast, democracy is the founding ideal of the United States. We base our whole system on freedom and democracy. Some of the people who are angriest today are angry because there is not enough democracy and freedom (in their minds). This is not the mindset of a people who would accept being ruled by a dictator.