Exit polls from 2016 showed that the 18 percent of voters who had negative views of both Hillary Clinton and Donald Trump broke heavily (47-30 percent) for the latter. In the latest NBC/WSJ poll, Joshua Green points out, voters who dislike both Trump and Joe Biden are backing the Democrat, 60-10 percent. I’d be awfully surprised if that margin holds up, or if Biden’s net-favorable rating (-4 in the poll) doesn’t get worse. But in what seems very likely to be a highly negative, character-based campaign, it’s a number to keep track of.