Most voters have negative feelings about both Hillary Clinton and Donald Trump. And a larger than usual percentage of voters are telling pollsters they wouldn't vote for either candidate. The latter logically follows from the first.

What is the magnitude of the non-support of the two major party candidates? Significant, I think. At this point in 2012 only 9 percent of those polled said they weren't voting for either President Obama or Mitt Romney, according to the RealClearPolitics average of recent polls. This year 15 percent in two-candidate pairings say they aren't supporting either Hillary Clinton or Donald Trump.

The effect is even more vivid when you look at the three-candidate polls conducted since mid-May including Libertarian Gary Johnson and the four-candidate polls conducted starting in June including Johnson and Green candidate Jill Stein. In both cases the results show 22 percent of voters not supporting either Clinton or Trump.

Of course inclusion of third and fourth party candidates in a poll's questionnaire tends to produce an overstatement of their actual support, since their names and parties are given the same prominence of those of the major parties' presumptive nominees. By the same token, the exclusion of their names tends to understate their support if it is anything more than minimal.

What I think is most interesting here is that we see between one-fifth and one-fourth of respondents who have passed screening questions indicating they're registered (or likely) voters being unwilling to back either major party's nominee. That's represents a breakdown of the strong and mostly stable partisan allegiances that have been prevalent over the last 20 years. Many people are apparently prepared to drop their usual partisan preference over their revulsion at or unease with their usual party's nominee.

Will such voters go to the polls and vote third or fourth party? Or will they skip voting altogether? Voter turnout has been declining in the Obama years, especially Democratic turnout, both in presidential years and offyears; it was up compared to 2008 and 2012 in Republican primaries this year, but down compared to 2008 in Democratic primaries.

By the way, none of these polls was conducted later than July 4, which means that no respondent had knowledge of FBI Director James Comey's statement on the Hillary Clinton email case July 5.