Some lawyers say a sitting president cannot be indicted, other lawyers disagree. Apart from that, does what they are saying apply to both federal and state indictments? I mean could the president be indicted by the state of New York, say?
Note the following argument:
the landmark 1819 case of McCulloch v. Maryland, which ruled that state officials cannot obstruct “the measures of a government [the federal government] created by others as well as themselves.” “In other words,” Kalt and Amar summarize, “a single state cannot use its power to derail the functioning of the United States.”
(Amar is a Yale constitutional law professor, Kalt, his student)
On the other hand, you have the argument by a Hofstra constitutional law professor that the 25th amendment can be applied when the President is occupied with a criminal case, ergo, the functioning of the United States can be carried on unimpared.
At the end-of-the-day there is no absolute answer as it is still being argued academically and has never been specifically settled by the courts.