Donald Trump is a weak president on the path to what can only be described as a failed presidency. I won't bore you with the extended "Neustadt is still the best" dive into the political science, especially since Matt Glassman already covered that exhaustively and there's little I can add to it.
That is not to say, Donald Trump's ideas are bad (they are) or that he is a terrible person (he is). It is to say that he is really, really bad at being president. He is an almost comically bad negotiator, and the one absolutely unassailable conclusion Neustadt drew is that bargaining and negotiation are the keys to a president getting anything he wants. Since the president lacks power to simply command Congress and other actors to obey him, he has to find a way to convince them that his interests are worth pursuing.
In that way and by any other measure, he simply is awful at this. A guy the media uncritically allowed to pitch himself as some kind of master Deal Maker is, in reality, so bad at negotiating that it's getting a little hard to believe. Alternating between braying invective and transparently insincere appeals for "unity" is a sign of how weak and ineffectual he is. Neustadt is an old piece of political science and many other interpretations of presidential power have since been written, but I am one of the many who believe he fundamentally got it right (if not in every detail). Presidents who can't negotiate are failures.
That said, I've been thinking a lot lately about how – now and in the future – to incorporate Trump into the minor national pastime of evaluating and ranking presidents. That's unimportant in the grand scheme of things. But other than looking at the small data set, declaring Trump an outlier, and pretending these four years didn't happen I see his presidency as incompatible with any attempt at analysis – including Glassman's (wholly accurate) application of Neustadt.
Here's the thing: Donald Trump isn't even trying to be president in any sense that the job of the president is understood. An analogy might illustrate my point best. Imagine you wanted to rank the (53 x 2) 106 quarterback performances in the Super Bowl. But you didn't have 106 quarterbacks – you had 105, and then this one guy who showed up on game day wearing a loincloth, swinging around a baseball bat, and making no effort to play the game at all. He simply showed up, preened for the crowd, and screamed "Fuck you!" at the referees for three hours.
In one sense, you could easily look at that list and say he is 106th of 106. But in another sense you can't even rank him on the same list as the others. It's not merely that he played a bad game (as players 104 and 105 obviously did). It's that he was playing an entirely different game that nobody else during, before, or since was playing. His goals and motives were wholly his own and largely inscrutable.
It is entirely possible that aside from Trump's commitment to rapacious tax cuts for the wealthy and his puerile obsession with The Wall, there is nothing he is even trying to do. In that light it is incorrect to say he's a weak, crappy president. He simply isn't the president at all in any meaningful sense. He spends most of his day doing nothing. He is on vacation more than he is in the White House. His goal seems to be nothing more than getting attention (at which he is very good, thus he probably considers himself a success by that criterion).
In the end it's an apples / oranges problem. Forty-four presidents were attempting to drive a bus, and then you have this other guy who wanted to blow up the bus and refused to drive it. It's not clear at all that the 45th guy even belongs in the conversation. There's a difference between doing something poorly and simply not doing it at all.