The Times reports.

What all of this probably means is that some critical number of independent voters decided they didn’t like the options the two parties had given them, and they were willing to go to the trouble of writing in a candidate who seemed to have a real chance of winning rather than pull levers A or B.

This was bound to happen somewhere. There was a time in America when our primary process made perfect sense, because most voters identified closely with one party or the other, and it was safe to assume that someone who wanted to participate would choose a team. In the 1950s, independents lagged behind both parties, making up less than a quarter of the electorate.