Two states are hard to poll accurately, probably because they have high rates of migration: Alaska and Nevada. In addition, Nevada has a high Hispanic population, which votes heavily Democratic. Based on early voting, it looks like 2016 will be a repeat of 2010 and 2012, in which Democrats outperformed Nevada polls by 10 and 3 percentage points, respectively.

In 2010, poll medians missed the victory of Senator Harry Reid (D) over Sharron Angle (R) by nearly 10 percentage points. In 2012, President Obama led Mitt Romney in early voting by 7.6% and ended up winning the state by 6.7%, more than his polling lead of 4%.

In 2016, as the Votemaster says, early voting is favoring Hillary Clinton nationwide. And in Nevada, where early voting ended on Friday, Clinton has outperformed President Obama. If her final total matches the 2012 result, it would be a 6-point performance over her polling median, Clinton +1%. In short, the Nevada bonus will be just about halfway between 2010 and 2016.

In the crucial Senate race there, the current median is Cortez Masto (D) +3.0%. It appears highly likely that this seat will go Democratic. That would bring the Senate Democratic/Independent total to a minimum of 47 seats (for easy reference, the RCP counter is here). In Pennsylvania, add McGinty, who is at +3.0%, to get 48 seats. To retain control, Republicans will need to hold Democrats to winning only one of the following five races: Indiana, Missouri, New Hampshire, North Carolina, and Wisconsin. That is an uphill climb for them.