IANAL, but there are lawyers who do not agree with the Office of Legal Counsel’s guidance that a sitting President should not be subject ot criminal indictment while in office. So I will leave argumentation to them and suggest a couple of other points that ought to be relevant.
First off, any political system in which a particular person of office becomes so central to the functioning of said system is deeply flawed and headed for trouble. In the absence of a means of calling bad behavior to account, it is simply a matter of time until someone takes advantage of that lack of accountability to engage in bad behavior.
To be sure, there is a defensible argument that a sitting President ought not be subject to harassment from minor nuisance lawsuits. However, on the one hand, courts have tools to deal with frivolous or malicious suits. And, on the other, if it is truly minor, then the distraction ought to minimal. What then about a situation where the matter is serious and likely to be time consuming (as, for example, were Trump to be charged with obstruction of justice.) I seems to me that there is a tool at hand to deal with such unlikely circumstances — the 25th Amendment. For whatever period of time the matter was under adjudication, the Vice President assumes the powers of the office and assures ongoing matters of policy and administration are attended to.
The cherry on the sundae is that the pernicious effect of the OLC opinion hold sway until challenged and tested in court. It is hard to imagine a set of conditions that would result in such a challenge and test.