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Six Consistently Close Races Will Probably Decide Control Of The Senate

Dan Sullivan won the Republican nomination for Senate in Alaska on Tuesday night, finalizing our cast of Democratic and Republican candidates for the most competitive Senate races in November. Republicans, despite some close calls, nominated candidates mostly in the mainstream of the GOP, avoiding the fringe candidates who have hurt the party’s electoral prospects in the past.

Republicans look likely to pick up seats in Montana, South Dakota and West Virginia — putting the party within three seats of the majority.

The map right now is simple: Control of the Senate will be decided in Alaska, Arkansas, Colorado, Iowa, Louisiana and North Carolina. Republicans must win at least half of these races.

Yet, we still can’t say with much confidence who will win the Senate. These are tight races.

In our latest FiveThirtyEight forecast, we gave Republicans no higher than a 60 percent chance of winning any of these six seats and no lower than a 40 percent chance. In the Huffington Post’s Pollster aggregates, no candidate in any of these races leads by more than 3.1 percentage points. All these races are too close to call.

The races have also been consistently tight. We’re not just looking at a fluke poll that shows a close election; voters seem to have held onto their opinions. The margin in these six races has shifted an average of less than 2 percentage points over the past six months, according to the Huffington Post Pollster aggregate. Since June 1, the races have shifted by only 0.7 points on average, and no race has shifted more than 2 points.

Here’s the state of things:

Alaska: Polls show Democratic Sen. Mark Begich holding his own against Sullivan despite President Obama’s dismal approval rating in Alaska (below 35 percent). Begich had a 2 percentage-point lead in the aggregate of polls six months ago. He’s now ahead by 3.1 points. Given the history of inaccurate polling in Alaska, a 3-point lead isn’t worth much. The FiveThirtyEight forecast in March gave Begich a 55 percent chance of winning, and in August it pegged his chances at 50 percent. We’ll have to see whether Alaskan Republicans coalesce around Sullivan.

Arkansas: Democratic Sen. Mark Pryor is hoping that his family name and Republican Rep. Tom Cotton’s very conservative record are enough to put him over the finish line in this rapidly reddening state. Pryor was down by 0.8 percentage points to Cotton in the aggregate of polling six months ago. He’s now down by 1.9 points. The FiveThirtyEight odds had Pryor at 30 percent in March and 40 percent in August. That would indicate a somewhat improved position for Pryor, though much of the shift reflects that FiveThirtyEight’s forecast weights polling more heavily as we get closer to the election.

Colorado: Democratic Sen. Mark Udall got the toughest possible opponent in Republican Rep. Cory Gardner. Udall was up 1.5 percentage points in the aggregate of polls six months ago and is now up 1 point. FiveThirtyEight has held Udall’s chance of winning consistently at 60 percent. If Republicans can win here in the fall, it would mark a turnaround from four years ago, when the GOP lost a hotly contested Senate race by just under 2 points. If the GOP wins a state like Colorado in November, it probably means Republicans will gain Senate control.

Iowa: Democratic Rep. Bruce Braley and Republican state Sen. Joni Ernst are matched up in the only open race on our list (there’s no incumbent on the ballot). It’s also the only seat where there has been significant movement over the past six months. Braley was ahead six months ago by 6.5 percentage points in the polling aggregate, but Ernst was ahead by 0.8 points on the night of her primary victory in early June. Ernst made up ground as she became better known, but she was also helped by Braley’s farmer “gaffe.” The race has remained stable over the summer, with Braley up 1 percentage point in the current aggregate. The FiveThirtyEight forecast gave Braley a 60 percent chance in June and a 55 percent chance in August.

Louisiana: Democratic Sen. Mary Landrieu is probably going to face a December runoff against Republican Rep. Bill Cassidy, as no candidate is likely to receive greater than 50 percent of the vote in November (Louisiana doesn’t hold separate primaries for each party. All the candidates run in one election, and if no one wins a majority of votes, the top two finishers advance to a runoff election). Landrieu was down in the polling aggregate for that runoff by 1.5 percentage points six month ago; she’s down 0.5 points right now. Her odds of winning, according to FiveThirtyEight’s forecasts, have stayed constant at 45 percent. Keep in mind, however, that predicting who will vote in the runoff may prove difficult. For example, African-American voters have made up a larger percentage of voters in many Louisiana runoffs compared with the preceding general elections.

North Carolina: Democratic Sen. Kay Hagan is trying to fend off Republican State House Speaker Thom Tillis, who leads North Carolina’s very unpopular General Assembly. Hagan was down by 0.5 percentage points six months ago and is up by 1.5 points now. In March, FiveThirtyEight gave her a 50 percent chance of winning, and it did so again in August. The complicating factor is Libertarian Sean Haugh, who is currently pulling in almost 8 percent in Pollster’s aggregate. But third-party candidates often fade during the campaign, and polling that doesn’t include Haugh has been at least a few percentage points better for Tillis.

Overall, these races have been tight as tick. With “gold standard” polling at a minimum, we shouldn’t be shocked to see polling move around a bit. The key will be to see whether either party or any of these candidates can pull away in the next few months. If not, we could be in for a long election night.

Harry Enten was a senior political writer and analyst for FiveThirtyEight.