Jonathan Bernstein: “Overall, it does seem to me that the Senate majority next year is as close to a toss-up as possible. Democrats need to gain four seats to reach 51. That’s not just a realistic possibility; it’s as likely as not.”“And at this point, there are far more known unknowns that could break the Democrats’ way than those that could favor the GOP, which makes up for a playing field (based on which states are holding elections this year) that still slants away from Democrats.”