An argument can be made after things like the second Iraq war that we have already entered the decadent empire phase of US history and the President effectively does have a great deal of dictatorial power. It's not supposed to be possible to wage a war like that without a congressional declaration, making such wars a pretty huge abdication of power by the legislative branch. If the President can just start a war on a whim, that power can be used to drag along the entire rest of the government.
Now, with ICE, we are establishing a lawless executive branch police force. This is just the unilateral power of the President to wage war coming home and being applied to domestic affairs. It will soon be possible, if it isn't already, for the President to order their own independent police to do anything, and if it is considered illegal the power of the pardon can be used to make that go away. The arbitrary power of the pardon is a pretty awesome power when you think about it.
When the ratchet gets far enough down this path we may indeed see a president remain in power forever like Xi Xinpeng. Trump may or may not be that person. If it's not him it might be the next, or the next. It could just as easily be a left-wing populist demagogue as a right-wing one depending on which way the winds happen to be blowing when the final ratchet click happens.
Rome continued to exist for quite some time after its Republic collapsed, but it was definitely the beginning of the end.