If U.S. President Donald Trump asked FBI Director James Comey to stop investigating former National Security Adviser Mike Flynn and his ties to Russia, that's obstruction of justice. But let's be clear: It's the impeachable offense of obstruction. It's probably not the criminal version of that act. With the evidence now available, it's extremely unlikely that an ordinary prosecutor could convict Trump.
This is an outstanding example of a crucial distinction that Americans and others badly need to keep in mind. High crimes and misdemeanors, to use the U.S. Constitution's phrase, aren't the same as ordinary crimes. What makes them "high" is their political character. High crimes and misdemeanors are corruption, abuse of power and undermining the rule of law and democracy. They don't have to satisfy all the technical aspects of an ordinary crime. And this act of Trump's, as described in a memo written by Comey first reported Tuesday by The New York Times, probably doesn't.
Start with the federal obstruction statute, 18 U.S.C. Section 1503. The first part of the law has to do with trying to influence jurors in the course of a trial; we can ignore it for our purposes.