Why do people worry about an imperial presidency?

My guess is that the imperial presidency is far down on the list of worries for most Americans. For those few that worry about it, it is likely because they do not like what the president is doing. Since the only way the US can have an imperial president is for the Congress to abdicate its constitutional power , maybe that is what they worry about, That is what I would worry about- a Congress that is afraid to take a stand because they would think it might cost them votes and they are more interested in keeping their job than in solving the country's problems.