From the report....
'The first specific criterion is the ability to take in important information and advice. To be capable of taking in new information to make decisions, given how that is one of the primary and most important roles of a president.
The second criterion is the ability to process that information unimpeded by emotional needs or false beliefs or the need to lie to yourself or others. The ability to simply use the information you have and process it in ways that are normal, unimpeded by all those other emotional factors and needs.
The third criterion is to be able to make sound, rational, reality-based decisions without undue influence by impulsivity, other false beliefs, delusions and conspiracy theories. It's the ability to stay with a decision in a stable way and not to go back and forth depending on the other influences you receive. In essence, to be sane, to be connected to reality.
The fourth is to not put yourself and others in danger. This includes not inciting people to commit dangerous acts. Not to engage in aggressive acts yourself. Not to threaten nations by inciting war. We have found that President Trump was not able to refrain from those acts in many circumstances. Trump has put himself and the nation in danger, and putting yourself or others in danger is also a very important criterion in determining a person's capacity to serve — in this case, Trump's fitness to be president. There is overwhelming evidence in the Mueller report showing that Donald Trump is not able to meet these criteria. Likewise, there is very little evidence showing that Donald Trump is able to meet those criteria.'