The final weekend before the midterm elections the race to control the Senate remains close enough that either party can still win. The Republicans have an edge, but certainly not an insurmountable one. Looking at the most recent polls. electoral-vote.com has the Republicans with 51 seats. This means that the Democrats would only have to win in one state where they are behind provided that they hold onto the seats where they have a slight lead and that Greg Orman caucuses with the Democrats if he wins.
There is far less quality polling in Senate races in a midterm election than in presidential elections, and a slight lead in the polls is far less predictive than a slight lead in a presidential election. If either party out-performs the latest polls by just a couple points the final result could be much more favorable than these predictions, for either party. Sam Wang pointed out the significance of so many races being close:
As I wrote last week, everyone’s calculations are, to an extent, built on sand. Historically, in any given year midterm polls have been off in the same direction by a median of 2 or 3 percentage points. Depending on the year, either Democrats or Republicans end up outperforming polls. In current poll medians, six races are within less than 2 percentage points: Alaska, Colorado, Georgia, Iowa, Kansas, and North Carolina. Therefore all six of these races could be won by Republicans…or all six could be won by Democrats.
The other races total 48 Republicans and 46 Democrats/Independents. Republicans are slightly favored to take control, since an even split of the six close races would give them the 51 seats they need*. However, the likely possibilities range anywhere from a Republican majority of 54-46 to a Democratic majority of 52-48. As of today, cranking through the math and the uncertainties gives a probability of 55% for a Republican takeover.
Nate Silver sees the Republicans as having a significantly higher chance at taking control of the Senate at 68.5 percent.
Among the reasons that the Republicans now have the edge is narrow leads in two states where the Democrats should be competitive, Iowa and Colorado. It is especially disturbing that a candidate as extreme as Joni Ernst can have the momentum in her favor in Iowa, moving to a seven point lead. There remains hope that the Democrats could still win one or both of these states, with early voters possibly favoring Democrats in Iowa. Campaigning by both Clintons and Elizabeth Warren might also help.
The Democrats still have a reasonable shot of maintaining control of the Senate due to unexpectedly competitive races in Kansas, Georgia, and Kentucky. The race in Kentucky is heating up with Democrat Alison Lundergan Grimes filing a suit to attempt to prevent Mitch McConnell distributing a mailer that it says amounts to illegal voter intimidation tactics.
One reason that the polls could be off by a few points is that the polls are weighted by who the pollster predicts will actually turn out to vote. Democrats hope that their ground game will tilt this in their favor, and are especially counting on their edge among women voters.