This article is from the archive of our partner National Journal

Senate Democrats are on the precipice of losing their majority. To understand why, look at Bruce Braley.

If the Iowa Democrat is defeated Tuesday, it won't be because of the insults he leveled against Chuck Grassley or the complaints he had about his neighbor's chickens, though neither helped. He'll lose because he couldn't break free of President Obama. 

Polls that show Braley trailing narrowly behind Republican Joni Ernst also demonstrate how much Iowans dislike Obama. Just two years ago, the president won 52 percent of the vote in Iowa and capped his reelection campaign with a rally in Des Moines. By October 2014, Obama's approval rating had dropped to 42 percent in a CNN poll and 40 percent in a survey from Fox News. An NBC News/Marist poll found that only 36 percent of likely voters in Iowa backed the president—barely more than the share who say they support Obama in the Republican strongholds of Arkansas and Kansas.

Certainly, Democrats argue and Republicans acknowledge that the electorate's opinion of Obama won't solely determine this week's results. But recent elections have demonstrated that Senate candidates who share a party with an unpopular president have—at best—a marginal capacity to win the votes of those who are unhappy with the White House.

And so this week, if Democrats somehow defy predictions and retain control of the Senate, they'll have done so by demonstrating an unusual, collective talent for withstanding political headwinds along the lines of some of their party's most celebrated victors of the last decade.

That—and not wandering chickens or ill-timed insults—is their biggest challenge on Election Day.

Senate elections have been driven increasingly by the national political climate rather than local issues. The trend started to be felt acutely in 2006, the last time the Senate changed hands. That year, Republicans discovered, among a host of other problems, that they couldn't persuade the public to look past their party's unpopular president.

George W. Bush was disliked in most states by then, including three he had won during his last campaign: Missouri, Montana, and Virginia. At a campaign speech in Virginia that year, Bush figuratively wrapped Republican Sen. George Allen in his arms. "George Allen and I have made our position very plain," Bush told a crowd. "Nobody has to guess where we stand."

Allen and his colleagues from Missouri and Montana ran ahead of Bush, persuading some people who didn't like the president to still vote for them, but it wasn't enough. They ultimately lost agonizingly close races that added up to give Democrats 51 Senate seats the next year.

The red-state-heavy list of Senate seats up in 2014 always meant that Democratic candidates would have to run in places where the president has long been unpopular. But in a handful of purple-state battlegrounds, the president's approval numbers have also slipped enough to cause real problems for Democratic candidates.

Indeed, Obama's ratings this year have dropped below the levels that troubled Republicans in 2006.

The NBC News/Marist polls show that in Colorado, an increasingly cosmopolitan state thought to define the country's demographic-led leftward lurch, Obama's approval stood at just 40 percent in October. Just 40 percent of likely voters also supported the president in North Carolina, a state Obama won in 2008 and lost narrowly in 2012. In New Hampshire, 39 percent of voters approved of Obama in the latest CNN poll.

Put another way, Democrats face a worse version of the same problem that burdened the GOP in 2006, when Bush's approval ratings fell to around 45 percent in those key tipping-point states.

Republicans say they've done more this election cycle than in previous ones to talk about local issues and prosecute a broader case against Democratic candidates around the country. But they've also plainly sought to maximize the impact of Obama's unpopularity on the election.

Within 24 hours of the president's October comments that his policies were "on the ballot" this fall even if he wasn't, multiple Republican candidates (including Senate Minority Leader Mitch McConnell in Kentucky) released TV ads using the tape to bind their Democratic opponents more tightly to the president. Ahead of the GOP wave election in 2010, the National Republican Congressional Committee used Obama in about one-quarter of its TV ads against House Democrats; in the last few weeks, the president has been in noticeably heavier rotation in the National Republican Senatorial Committee's attack spots.

Somehow, Democrats are still in contention, narrowly, to hold the Senate on Election Day. If they do, the results in several states will have to look a lot like they did in Missouri in 2012.

That year, Democratic Sen. Claire McCaskill won 20 percent of Mitt Romney voters in her state, according to exit polls, on her way to a second term. That's a high-water mark for endangered Democrats in the last two sets of exit polls, but it's along the lines of what Democrats may need to attract from Obama disapprovers to win this year.

But McCaskill had something that Democrats up for reelection in 2014 lack: a Republican challenger as embarrassing as Todd Akin, the man who suggested women were capable of preventing pregnancy by rape. GOP primaries were hard-fought, rocky affairs in this year, but Senate Republicans emerged with a strong slate of nominees.

A few other Democrats in recent elections have gotten close to McCaskill's performance among those who dislike Obama, but, like her, Nevada's Harry Reid and Indiana's Joe Donnelly were running against flawed GOP candidates. (Sen. Heidi Heitkamp of North Dakota apparently did well with Romney voters in her upset 2012 win, but there were no exit polls in the state that year.)

So while the Republican brand is not particularly well-liked nationwide, the GOP's 2014 candidates don't have the personal baggage that helped offset the drag of Obama's unpopularity in the past.

That Democratic candidates have managed to remain competitive this year under these circumstances is impressive. But it might not be enough, especially for contenders like Iowa's Braley, whose many problems (seen by at least one observer as fatal) will be eclipsed by the president's negatives as the determinative factor on Tuesday night.

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

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