Sam Wang is a mega-wonk at Princeton, whose analysis has been more favorable to Dems this cycle than fellow wonk Nate Silver, who adjusts polls for state and other factors (fundraising).  

That changed this week, even factoring in the Kansas debacle for the GOP, due to a shift in Alaska and Colorado towards GOP. Wang writes at the Princeton Election Consortium:

Our time window is currently to take the last 3 polls or the last 2 weeks of data, whichever is more, for each state. This measure takes a little while to move, but when it does, that’s meaningful. Statistically, we are now at the most Republican-leaning end of the range that we have seen in the entire graph.The dip in June looks better for Republicans, but keep in mind that on September 3rd, the Meta-Margin jumped by 0.8% when Chad Taylor (D-KS) dropped out of the race. Subtracting that gives a better feeling for where we’re at, not counting Kansas. In short: as a group, Republican Senate candidates outside Kansas are at an all-time high. (emphasis added)