Polls giving GOP the edge in Senate takeover

Joni Ernst, Iowa Republican Senate candidate, talks with a voter in the Pork Tent at the 2014 Iowa State Fair in Des Moines, Aug. 8, 2014.
Tom Williams | CQ Roll Call | Getty Images

It was a very good weekend for Republicans' hopes of taking back the Senate in November. Topping the list of GOP goodies: Joni Ernst now has a 6-point lead over Bruce Braley in the Iowa race to fill retiring Democrat Tom Harkin's seat.

According to the latest Des Moines Register poll, Ernst leads 44 percent to 38 percent in a race that was once viewed as close to a sure thing for Braley and the Democrats. Braley is now not even winning his own congressional district and is being weighed down by his support for Obamacare, among other problems.

In Louisiana, a CNN/ORC poll showed incumbent Democrat Mary Landrieu falling to well below the 50 percent threshold needed to avoid a Dec. 6 runoff. In the runoff, Landrieu trails Republican Bill Cassidy 50 percent to 47 percent among likely voters, though she leads by 6 among registered voters. The Louisiana contest now seems likely to hinge on massive get-out-the-vote operations for the runoff.

In North Carolina, meanwhile, a CNN/ORC poll showed incumbent Democratic Sen. Kay Hagan leading GOP challenger Rep. Thom Tillis by just 3 points, 46 percent-43 percent. Tillis is hindered somewhat by Libertarian candidate Sean Haugh taking 7 percent. Still, Tillis is very much in striking distance.

A Tillis win would come close to guaranteeing Republicans pick up the six seats they need to control the Senate next year.

Read MoreWhat Wall Street should expect from the next AG

The GOP is virtually assured pickups in open seats in Montana, South Dakota and West Virginia and is likely to defeat Democratic Sen. Mark Pryor in Arkansas. Polls now also show Republican Dan Sullivan leading Alaska Democratic Sen. Mark Begich. Landrieu would put the total at six and Tillis would bump the GOP gain up to seven and provide a buffer should independent Greg Orman defeat incumbent Republican Sen. Pat Roberts in Kansas and go on to caucus with Democrats, as many expect.

Kansas, in fact, may be the Democrats only opportunity to defeat a Republican. Sen. Mitch McConnell, R-Ky., appears headed to re-election and businessman David Perdue seems likely to hold GOP Sen. Saxby Chambliss' seat in Georgia.

Republicans could also wind up picking off a Democratic seat in Colorado where Sen. Mark Udall trails GOP Rep. Cory Gardner.

All of the major political prediction models are now forecasting increasing odds of a GOP takeover. The Washington Post's Election Lab gives Republicans a 76 percent chance to take the Senate. FiveThirtyEight puts the GOP odds at 60 percent and The New York Times' model has Republicans at 67 percent.

Why is this happening?

In part, the odds just reflect the attractive terrain the GOP has always enjoyed in the 2014 midterms. This advantage will flip in 2016 when the GOP will have to defend vulnerable tea party incumbents elected in the 2010 wave year. The GOP in 2014 is also enjoying the typical advantage held by the opposition party in the sixth year of a president's second term.

Read MoreAll signs point to Jeb Bush prepping for 2016 presidential run

Add to that a president with woefully low approval ratings and heavy spending by GOP groups such as America Rising on opposition research on Democratic candidates like Braley and you have a recipe for Republican takeover. In fact, it would be a big rebuke to Republicans if they fail to take the Senate and would likely presage a very strong year for Democrats in 2016.

So is there anything that can stop Republicans from gaining the majority in November? One possibility is sustained bombing raids against Islamic extremists in Iraq and Syria boosting Obama's approval rating and limiting his drag on Democratic candidates. But that's a relatively low possibility.

Read MoreBill Clinton: I know why US incomes are stagnant

It also seems clear that there will not be a great pickup in the economy in the month left until Election Day, boosting people's spirits and benefiting the incumbent White House party. Friday's September jobs report is expected to show a gain of around 200,000, a solid number but hardly a political game changer. Meanwhile, wage gains, which drive voting behavior much more than top-line jobs figures, remain stuck at or below the rate of inflation, leaving many voters feeling stuck and frustrated, a bad scenario for the party holding the White House.

Democrats, for now, have to bank on Roberts losing in Kansas while Landrieu and Hagan hold on. Otherwise, turn out the lights because the party's over. Until 2016.

—By Ben White. White is Politico's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet Politico Morning Money [politico.com/morningmoney]. Follow him on Twitter @morningmoneyben.