In one form or another, all point toward a Republican takeover of the Senate, although their leanings vary significantly. The Post’s Monkey Cage is by far the most bullish, saying that it is more than 80 percent likely that the Republicans will take control of the Senate in January. Others suggest that the battle will continue to rage until November.

Republicans need to win a net of six seats to take control. Three states are considered almost certain to switch from Democrat to Republican: Montana, South Dakota and West Virginia. It’s relatively easy to assume they will gain one or two. The debate is about how many more Republicans will win beyond that. They have plenty of options but their victories must come either by defeating Democratic incumbents in red states or picking off seats in blue or purple states that Obama and the Democrats have been winning in presidential elections.

To give some idea of the differences in current assessments of the outlook, the Upshot has published a chart summarizing what the six election forecasters say about 10 competitive Senate races (beyond Montana, South Dakota and West Virginia).