Regardless of what the FBI finds, if Kavanaugh is confirmed, most Democrats will believe we have a sexual predator on the Supreme Court. I feel totally comfortable using the word “most”.
If the FBI finds nothing, but possibly because they were instructed not to look for certain things that would be reasonable for such an investigation, I’d have a hard time not joining that number, though I’m not a Democrat anymore. As I said, cover-ups scream “guilty” even when it’s not true. The “dirty defense” as you call it would be entirely to blame for people’s misperceptions if he’s actually innocent.
I don’t believe most Democrats would trust the results of the investigation regardless of its credibility. That’s just where we are now. The left has joined the right on the crazy train and people’s beliefs align more with their ideology than an honest assessment of the facts.