He should have simply said “no comment.”

When I was a federal prosecutor in South Florida, one of my roles was to field inquiries from the media about potential investigations pending in our office. My response was always some version of “no comment.” It got to the point where most reporters would simply call and ask “can I go ahead and put you down for ‘no comment,'” before I even had a chance to speak.

That is because when it comes to pending investigations federal prosecutors and agents almost always have only two good options: indict or be quiet. Talking publicly about a matter is not an option because doing so offends basic notions of fairness and due process. It creates incredible potential for misimpressions and gives the impacted parties no ability to meaningfully address allegations.

Internal rules of the Department of Justice and long standing practice reflect these concerns. The U.S. Attorney’s Manual (Rule 1-7-530), the handbook that guides nearly every decision of a federal investigation, provides that personnel “shall not respond to questions about the existence of an ongoing investigation or comment on its nature or progress.”

This rule is especially true when it comes to political investigations that could impact elections. For instance, in the handbook produced by the Justice Department’s Public Integrity Section on Election Offenses there is an entire section titled “Noninterference with Elections,” in which the authors, high ranking Justice Department officials, explain that in election investigations “federal law enforcement personnel should carefully evaluate whether an investigative step under consideration has the potential to affect the election itself.”

The authors explain the concern that making public investigative issues “runs the obvious risk of chilling legitimate voting and campaign activities…and also runs the significant risk of interjecting the investigation itself as an issue…”

Sound familiar?

Director Comey’s recent letter is, regrettably, a case study of why it’s such a bad idea to talk about investigations publicly. After the FBI had reviewed tens of thousands of Clinton emails, Director Comey announced the FBI found no basis for further criminal review because “no reasonable prosecutor” would pursue the matter.

His recent letter does not change that conclusion in any way, and he says so. He acknowledges the Bureau has not even reviewed the emails; have no idea if they are even Hillary Clinton’s; and can’t explain if they have anything to do with the issues they were previously reviewing. He even expresses his concern that his statement may create a “misleading impression” and will run the “significant risk of being misunderstood.”

So why say anything?

Because Comey felt compelled to make a statement on the eve and in the vortex of a hotly contested national election, it has become a dominant campaign issue. Trump and the Republicans are arguing that this otherwise mundane statement is grounds to convict and charge (apparently in that order) Hillary Clinton for high crimes. Democrats are responding by demanding all the investigative materials be released so the public can see that there is no there there.

Of course, no additional information will be forthcoming from the FBI because that would, well, violate FBI rules against commenting on investigations.

See the problem?

Director Comey’s announcement was a clear mistake and contrary to Justice Department precedent and, more importantly, good judgment. I suspect Comey, who is not a partisan hack, made the decision more out of concern for himself than for anyone else. While it may throw the election into chaos, it serves as a CYA memo that he can point to when the Republican Congress continues their partisan hearings next year. He will be able to blithely claim all he did was release information, and how people reacted was not his responsibility.

But for Americans hoping for an election about issues and not distractions, Director Comey did a real disservice.