From Cato’s Julian Sanchez:
This was, at least originally, both a criminal and a counterintelligence investigation. And there are a number of questions left unresolved that don’t necessarily relate to criminal conduct, but are highly significant from a counterintelligence or national security perspective. One question is whether Russia had some form of “kompromat” or other leverage over Trump—which might help to explain why they were so eager to promote Trump above other Republican contenders. That could be true without Trump having committed any crime (or any crime directly related to the election) but it would obviously be quite urgent for the public to know about.
There are also questions about the campaign’s stance toward Russian interference that go beyond direct “coordination” or “conspiracy.” We know the campaign was eager to make use of hacked Democratic e-mails, and that Trump and his surrogates sought to cast doubt on Russia’s responsibility for that intrusion long after the Intelligence Community considered these to be established facts. If the Trump campaign knew or believed that Russia was indeed responsible at the time, that might not be criminal, and it might not amount to “conspiracy”—but it would be extremely damning all the same.