Nate Silver: “First, the macro path. As I mentioned, Democrats would become favorites to take the Senate if they won the overall popular vote for the House by more than about 11 points. At that point, the tailwind would simply be so strong that Democrats would probably find a way to win all or almost all of the toss-up races… We wouldn’t bet on Democrats winning the House popular vote by 11 points, which would be an overwhelming margin — the most lopsided margin for either party since 1982. But considering that they’re already ahead by 8 or 9 points right now, it can hardly be ruled out.”

“Or, the Democrats could win by means of the micro path and just have the coin come up heads in a lot of the toss-up races, even if the overall political environment isn’t any better for them than we’re currently projecting. In our Classic forecast, there are 11 seats that each party has at least a 10 percent chance of winning: Arizona, Florida, Indiana, Missouri, Mississippi, Montana, North Dakota, Nevada, Tennessee, Texas and West Virginia. Democrats need to win eight of those 11 to take the Senate.”