Democratic pollster Nate Silver's models have been trending the GOP's way for months and his latest effort shows a GOP gain of more than 50 seats for the first time.

Republican chances of taking over the House are now up to 80 percent, according to the FiveThirtyEight forecast model; they had been 75 percent two days ago.

In an average simulation, the model projected that the Republicans will control 230 seats when the new Congress convenes in January; that would reflect a 51-seat gain from their current standing and would be close to the 54-seat gain that they achieved in 1994. This is the first time we have published a forecast putting the Republican over-under line at a number higher than 50 seats.

As we remind our readers with each update, there is considerable uncertainty in the forecast. Democrats have a 20 percent chance of holding the House - but Republicans have a 30 percent chance of winning at least 60 seats, a 12 percent chance of winning at least 70 seats, and a 3 percent chance of winning 80 or more seats. We would advise against interpreting our forecast as a prediction that Republicans will win some particular number of seats. Instead, it should be thought of as being equivalent to a point spread.