If there was no evidence of criminal activity, why all the immunity?

That is the awkward question that William McGurn asks in a Wall Street Journal op-ed today...

Why did Cheryl Mills require criminal immunity?

This is the irksome question hanging over the FBI investigation into Hillary Clinton’s home-brew server in the wake of news that Ms. Mills was granted immunity for her laptop’s contents.

Ms. Mills was a top Clinton aide at the State Department who became Mrs. Clinton’s lawyer when she left. She was also a witness, as well as a potential target, in the same FBI investigation into her boss’s emails. The laptop the bureau wanted was one Ms. Mills used in 2014 to sort Clinton emails before deciding which would be turned over to State.

Here’s the problem. There are two ways a witness can get immunity: Either she invokes the Fifth Amendment on the grounds she might incriminate herself, or, worried something on the laptop might expose her to criminal liability, her lawyers reveal what this might be before prosecutors agree to an immunity deal.

As with so much else in this investigation, the way the laptop was handled was out of the ordinary. Normally, immunity is granted for testimony and interviews. The laptop was evidence. Standard practice would have been for the FBI to get a grand-jury subpoena to compel Ms. Mills to produce it.

Andrew McCarthy, a former U.S. attorney, puts it this way: “It’s like telling a bank robbery suspect, ‘If you turn over that bag, I’ll give you immunity as to the contents’—which means if the money you robbed is in there, I can’t use it against you.”

The Mills immunity, which we learned of on Friday, has unfortunately been overwhelmed by the first Trump-Clinton debate. But the week is still young. On Wednesday, Congress will have an opportunity to put the Mills questions to FBI director James Comey when he appears before the House Judiciary Committee.

Back in July, Mr. Comey must have thought he’d settled the issue of Mrs. Clinton’s emails with a grandstanding press conference in which he asserted “no reasonable prosecutor” would bring a case against her based on what the FBI had found. In so doing, he effectively wrested the indictment decision (and any hope for political accountability) from the Justice Department. Plainly even his own agents weren’t buying, given that Mr. Comey later felt the need to issue an internal memo whining that he wasn’t being political.

Now we learn about the multiple immunity deals. Immunity in exchange for information that will help make the case against higher-ups is not unusual. Even so, the Mills deal carries a special stink.

To begin with, Ms. Mills was pretty high up herself. As Mrs. Clinton’s chief of staff, she was in the thick of operations. In 2012, while working at State, she traveled to New York to interview candidates for a top job at the Clinton Foundation.

More disturbing still, not only was Ms. Mills granted immunity for the content on her laptop, she was permitted to act as Mrs. Clinton’s attorney even though she herself was also a witness in the investigation.

This was allowed in part because she told the FBI she knew nothing of Mrs. Clinton’s private server until after she’d left the State Department. But this claim is suspect and contradicted by emails that have since emerged. These include one to Huma Abedin asking, “hrc email coming back—is server ok?”

The special treatment accorded Ms. Mills also reeks on a more fundamental level. As a rule, the Justice Department is aggressive about going after lawyers for any perceived conflict of interest. This would include, for example, a lawyer who wanted to represent different parties in a trial.

By giving Ms. Mills a pass to serve as Mrs. Clinton’s attorney in an investigation in which she was a material witness, Justice allowed her to shield her communications with Mrs. Clinton under attorney-client privilege. Indeed, Ms. Mills invoked that privilege during her own FBI interview.

Imagine Tom Hagen, the mob lawyer played by Robert Duvall in “The Godfather,” discussing with Don Corleone who was to get whacked—and then invoking the lawyer-client relationship to hush it up. Think of it this way and you begin to get the picture.

For those who think the fix was in from the start, Ms. Mills’s presence at Mrs. Clinton’s FBI interview, along with nine other people (not including the two FBI agents) is further evidence of a circus. Judiciary Committee members might do well to ask Mr. Comey why Ms. Mills and so many others were allowed to sit in on that interview.

In short, far from resolving Mrs. Clinton’s email case, the handling of the investigation has provoked questions about integrity of both the FBI and Justice. The big question for Mr. Comey remains this: