Those numbers matched up almost exactly with how voters felt about Indiana Gov. Mike Pence (R), Donald Trump's running mate. When Pence addressed Republicans at their party's convention in July, he joked that not many in the convention hall even knew who he was.
One potential reason for Kaine's lackluster polling in particular: More than 6 in 10 Democrats hadn't heard of him, or didn't know enough about him to make a decision. So he's not well known -- and still isn't; that means he isn't particularly well liked (or -- silver lining! -- strongly disliked.) Kaine seems to be more of a blank slate, or background noise, than an immediate assets to Clinton's campaign.
As my Fix colleague Aaron Blake so succinctly put it, 2016 is the year of boring vice-presidential picks.
Fix Boss Chris Cillizza thinks that's exactly the way the presidential candidates want it to be. Trump and Clinton are two of the least-liked major-party presidential nominees in modern history.
As a result, both have framed the election as a referendum on the other's deficiencies. It's a loud, messy and dirty election at the top of the ticket, so why not have someone quiet, bland and, yes, boring to balance that out?
Of course, maybe we're spending much ado about nothing analyzing how voters feel about their party's vice-presidential picks: A July Washington Post-ABC News poll found the vast majority of voters said that whoever the candidates pick for a running mate wouldn't play a big role in their decision at all. So far, so true.