This article is from the archive of our partner National Journal

Despite the consensus that Republicans hold an advantage in the battle for Senate control, pundits have reached different specific conclusions. Roll Call's Stuart Rothenberg sensed a significant wave emerging, recently predicting Republicans would pick up "at least" seven seats, with the potential for even more. Other Senate modelers have tempered their forecasts recently, giving the GOP a slight edge but improving Democrats' odds based on favorable polls in many of the key states.

The biggest question is, how much do forecasters weigh the national environment, which is looking toxic for Democrats, against the individual state-by-state polls, some of which contain favorable news for specific Democratic candidates? That's been an added challenge this year, thanks to the proliferation of public polls with questionable methodology that can mislead more than inform readers.

But there have been clear trends that have emerged over the summer, even as the overall Senate outlook hasn't changed all that much. Right now, Republicans are likely to pick up anywhere from five to nine Senate seats, with the most critical races taking place in traditional battleground states.  

Here are the three biggest takeaways for the home stretch:

1. Red-state races are trending away from Democrats. If Republicans sweep the races in states that Mitt Romney won by double digits, they'll win a majority without needing to prevail anywhere else.

We're seeing two different types of Senate races develop—those in the deeply conservative states that Romney carried, and those in the perennial battlegrounds that President Obama won. And while the races in the swing states remained stable over the summer, Republicans made significant gains in more friendly territory that suggests (at least) a red-state wave is building.

In Kentucky, Senate Minority Leader Mitch McConnell has pulled ahead of his Democratic challenger, Alison Lundergan Grimes, by 4 to 8 points in public polling. With disaffected Republicans starting to come home to McConnell and coal country looking problematic for Grimes, the path to a Democratic victory is looking slimmer. In Georgia, public polling has been more volatile, but Republican David Perdue now holds a 6-point lead in the Huffington Post polling average. And even if Democrat Michelle Nunn finishes in first, the race heads to a January runoff if she doesn't win 50 percent of the vote—a contest where the lower turnout would favor Republicans. Meanwhile, both red-state challengers have resorted to attacking Obama in ads, a surefire sign that the president's unpopularity is a weight on their shoulders.

That same dynamic is boosting the fortunes of challengers against well-known incumbents in conservative states. Rep. Tom Cotton hasn't run the strongest Senate campaign in Arkansas, but he's nonetheless opened up a small lead against Sen. Mark Pryor. In a state where the president's approval rating barely hits 30 percent, it will require a significant level of crossover voters for Democrats to pull off the victory. In Louisiana, Sen. Mary Landrieu hasn't come close to 50 percent in public polls, and has been facing negative publicity about charging taxpayers for past campaign trips. She can't afford any mistakes as she prepares for a December runoff against Rep. Bill Cassidy. Her biggest saving grace could be if Republicans comfortably win the Senate on Election Day, and GOP voter anger subsides for her runoff contest. That's still a long shot.

The most notable Republican movement is in Alaska, where polls show GOP nominee Dan Sullivan with momentum since locking up the nomination. Democratic Sen. Mark Begich has run a shrewd campaign, with ads portraying him as best attuned to Alaska's interests. But he ran into trouble after airing—and later pulling down—a controversial ad accusing Sullivan of being soft on crime. The family of the victim referenced in the ad complained about the accuracy of the spot, and Begich quickly took it down. The flap dented Begich's squeaky-clean image, drawing outsize coverage in the Alaska press.  

One X-factor: GOP Sen. Pat Roberts in Kansas, whose race wasn't on either party's radar screen until recently. But his poorly run campaign and low approval ratings could make him vulnerable to deep-pocketed independent candidate Greg Orman, who has emerged as the de facto choice for Democrats. But if outside groups spend money and make the contest a referendum on partisan control of the Senate, odds are in Roberts's favor. It's still difficult to see Republicans sweeping red states, but losing in a state that Democrats haven't carried since 1932.

2. But in swing states, Democratic attacks have made their mark, giving them a fighting chance to maintain their majority.

At the same time, Democrats have been effective in raising the negatives of several of the GOP's leading recruits—Joni Ernst in Iowa, Cory Gardner in Colorado, and Thom Tillis in North Carolina. These are the contests that will determine if the sour public mood will lead to a Republican wave, and Democrats have relentlessly portrayed them as ideologically disconnected from the states they're running in.

In Iowa, the much-maligned Democratic nominee Bruce Braley holds stronger favorables than Ernst in both public and private polling—by portraying the state senator as too fiscally conservative for the populist state. Notably, in her latest ad, Ernst responds directly to accusations that she wants to privatize Social Security. It's a clear sign the attacks resonated. Tillis, whose fundraising has lagged behind expectations, has been hammered by millions of dollars in outside money casting him as too extreme for the state. He now trails Sen. Kay Hagan in public polling. And in Colorado, Democrats bet that women's issues would be particularly potent to use against Gardner, whose past vote for a "personhood" amendment restricting abortions has become the subject of numerous outside attacks. Gardner has been nimbly responding to the attacks, backtracking on his past positions and supporting over-the-counter access to contraceptives. But when you're playing defense—especially on social issues, a traditional Democratic strength—you're usually losing.

All three of these races are winnable for Republicans, thanks to the difficult national environment for Democrats. In all these races, the attacks have stunted the standing of the challengers, but haven't boosted the incumbents' numbers much. But they're also illustrative of how the damaged Republican brand is causing headaches for otherwise capable candidates in swing states. If Republicans come up empty in the traditional battlegrounds in a midterm election where most of the national indicators are in their favor, it's a glaring warning sign for their prospects in 2016.

3. There's a national wave if Republicans pick off two of the three battleground states: Colorado, Iowa, and North Carolina.

There's been a largely academic debate taking place over what constitutes a wave election. In July, I wrote about the signs of a wave increasing—and the macro-indicators are looking more favorable for Republicans since then. Most national pollsters are now showing Republicans with a clear edge on the generic ballot, while President Obama's approval rating continues to stagnate. In the latest NBC News/Wall Street Journal poll, Republicans held significant leads on the question of which party is best able to handle the economy, national security, immigration, and taxes. The GOP's biggest weaknesses were on social issues, where Democrats hope to exploit an already-sizable gender gap, and the party's overall image.

In our polarized political times, the national mood plays a dominant role in shaping the results of the midterm election. In Senate races, candidate quality clearly matters, but there are fewer split-ticket voters than ever before. If there's a national wave sweeping Republicans into office, you'd expect to see it emerge in three perennial bellwether states where Republicans recruited credible challengers: Colorado, Iowa, and North Carolina. So far, these races are either tied or Democrats hold a small advantage.

If undecided voters break against the governing party, as they often do in wave elections, those advantages could quickly dissipate. That would be consistent with the patterns of past wave years, where the incumbent is "stuck" at a certain level of support and a disproportionate share of late-deciding voters back the challenger. But if Democrats can effectively disqualify the GOP challengers to hang on, it's a sign the environment isn't quite as favorable for Republicans as things currently look. 

This article is from the archive of our partner National Journal.

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