Nate Silver today:
The most unambiguously bearish sign for Mr. Romney are the poor polls he has been getting in swing states from pollsters that use a thorough methodology and include cellphones in their samples.
There have been 16 such polls published in the top 10 tipping point states since the Democratic convention ended, all conducted among likely voters. Mr. Obama has held the lead in all 16 of these polls. With the exception of two polls in Colorado — where Mr. Obama’s polling has been quite middling recently — all put him ahead by at least four points. On average, he led by 5.8 percentage points between these 16 surveys.