ABC
Silver, whose fame grew during the 2012 presidential election, gives Republicans about a 60 percent chance of re-taking the Senate.
Republicans need to swing six seats to re-capture Senate control. They're on track to win in West Virginia, South Dakota, Montana, and Arkansas, according to Silver. Four states are toss-ups - Louisiana, North Carolina, Alaska, and Michigan. The most likely path to victory, then, for Republicans is swinging the four seats in which they're favored and winning two of the four toss-up seats. Polls have continued to show a large Republican advantage in states with open Senate seats.
There are also three Democratic-leaning seats - in Colorado, New Hampshire, and Iowa - the GOP could plausibly win. In the end, Silver said, Republicans could swing as many as 11 Senate seats. Then there's the caveat - Republicans are facing significant challenges in Georgia and in Kentucky.
You can read Silver's whole forecast here, and watch his appearance on ABC's "This Week" below: