Analysis: Attack ads aren't driving Obama's and Romney's numbers down

NBC also reported that the “very negative” ratings for both candidates have increased to “all-time highs” in the most recent poll, including 32 percent who now view the president very negatively.

But a more complete examination of the NBC/Wall Street Journal results shows that while the negative ratings of both candidates have increased slightly in July, the degree of change is modest…

The very negative ratings for both men have risen — to 32 percent for Obama and 24 percent for Romney in July — but the changes have played out gradually over the last four months and do not appear to represent sudden jumps.

It is also worth noting that the candidate ratings from the previous NBC/Wall Street Journal polls represented the views of all adults, while the July numbers were calculated among self-reported registered voters only (typically about 80 percent of all adults). Since nonregistered adults typically skew Democratic, their exclusion for the first time in July may explain in part the apparent upward trend in Obama’s very negative rating.