The history of the downfall of much greater men than Trump during the 20th century involved what they did during an investigation into allegations of misconduct rather than the allegations themselves. Nixon ended up disgraced because he had knowledge of a crime and tried to cover it up. Bill Clinton got it for lying under oath on the witness stand.
And for Trump, only time will tell whether his actions finally catch up to him. For out of the jumble of incidents outlined in Volume II of Mueller’s report that covers the obstruction of justice investigation, there are two different instances that really stand out as obstruction without needing to construe intent.
The first, and most obvious, instance is when Trump went back to Mr. McGahn to persuade him to claim to investigators that he never attempted to persuade him to have Special Council Mueller removed for conflict of interest, when Trump had previously tried to persuade McGahn to do so (according to Trump, bad blood exists between he and Mueller that predates the investigation).
The second one is more subtle, involving Cohen’s testimony to Congress, ensuring that their stories were straight, and coaching Cohen for his interview with investigators.
The report also vaguely refers to instances where “the word got out” to potential witnesses to not cooperate with the investigation. There isn’t any detail on this one about who did the spreading of “the word,” but we know who the ringleader is in Trumpland.
The bottom line is that Trump asked McGahn to lie to investigators. In Plain and Ordinary Ville where I live, it doesn’t matter why one would ask a witness to lie, there would indeed be legal consequences for doing so. The name Jesse Smollett comes to mind here.
Trump might be the President, but he isn’t above the law, and asking someone to lie to the FBI is obstruction.
As a side note here, Trump is certainly apt at acting guilty when he isn’t.