The quest for further FBI investigation into Kavanaugh's background

The Dems want the FBI to investigate Dr. Ford's allegations of attempted rape. Grassley says that's not something for the FBI. Some are saying the White House has to request it. Here's former FBI Director James Comey on the matter:

“I think based on past practice that would be up to the White House to ask if they wanted additional background investigation work done by the FBI,” Comey said with regard to the Kavanaugh situation. “The FBI traditionally does criminal investigations – that’s not what we’re talking about here. This is where the FBI at the request of a sponsoring agency, in this case the White House, does investigations to understand someone’s background or reputation. And so, my understanding is, in the past, if we’re asked to do supplemental work, we would do it.”

  St. Louis Public Radio

I would think that, a background investigation being standard for considering an appointment to the Supreme Court, and the FBI already having done one, simply putting Dr. Ford's letter in their discovery file would be incompetency at best. If new information comes to light, shouldn't it be as mandatory as the initial investigation in the first place? Aren't all investigations reopened in light of new information? Particularly if the new information is in regard to a possible crime? WTF?

P.S. The Comey interview audio is here.