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As the 2014 midterm election campaign heats up, all indications are that Democrats are headed for a trouncing at the hands of Republicans.

Most political prognosticators now give the GOP a better-than-even chance of picking up the six seats it needs to win control of the Senate, and the party is expected to expand its majority in the House.

The Republican gains may not match those of the Tea Party wave of 2010 that cost Democrats the House and their filibuster-proof majority in the Senate, but it likely will be enough to make President Obama's final two years in office even more of a headache than the last four have been.

There are many factors fueling the GOP's advantage, but the most striking difference between 2014 and 2010 is that the economy is not one of them. Both the unemployment rate and layoffs are way down, but Democrats by and large are not getting the credit for it.

Here, then, are the reasons Democrats could be in for another "shellacking" in November:

The Map

RealClearPolitics.com

Democrats always knew 2014 was going to be a tough Senate election for a simple reason: They have to defend a bunch of seats held in deeply red states that Obama lost in the last two presidential elections.

The three seats the party has all but conceded to Republicans are in South Dakota, West Virginia, and Montana, where the departures of long-serving Sens. Tim Johnson (S.D.), Jay Rockefeller (W.Va.) and Max Baucus (who became ambassador to China) pretty much doomed Democrats' chances of winning. Democrats initially had hopes they could hold onto Montana, but their nominee, John Walsh, withdrew from the race last month amid a plagiarism scandal.

With those three gone, Democrats have incumbents up for re-election in another four states that Mitt Romney won in 2012: Alaska (Mark Begich), Arkansas (Mark Pryor), Louisiana (Mary Landrieu), and North Carolina (Kay Hagan). Those races are all considered toss-ups, and Republican victories in three of them would give the GOP the Senate.

Republicans have also expanded the map to make competitive runs in Iowa and Colorado, two swing states that Obama won in 2012. Democrats, meanwhile, have only two shots at snagging Senate seats currently held by Republicans, and both of those – in Kentucky and Georgia – are in red states where they begin at a disadvantage.

On the House side, redistricting that occurred after the 2010 census has reduced the number of competitive races, helping Republicans lock in their majority.

The Unpopular President

Gallup.com

In the sixth year of his presidency, Obama is plainly a drag on Democratic candidates in most races. His national approval rating in the Gallup poll has hovered near 40 percent all summer, with a majority of voters disapproving of his performance in office. The president's numbers are even worse in the red states that are home to most of the competitive Senate races, leading to an avalanche of television ads linking Democratic candidates to the unpopular Obama.

The History

Even if Obama had better standing, his party would begin the midterm election in his second term at a disadvantage. That's because of the historical phenomenon known as the "Six-Year Itch," in which voters who have tired of the president's party have responded by voting against it in the midterm elections. According to electoral forecaster Charlie Cook, the president's party has lost an average of five Senate seats and 29 House seats over five of the six midterm elections of second-term presidencies since World War II. The major exception to that came in 1998, when President Bill Clinton and congressional Democrats benefited from a voter backlash to the GOP's impeachment drive (which largely explains why Democrats this year have been so keen on accusing Republicans of wanting to impeach Obama.).

And with the recent exception of 2006, when President George W. Bush's unpopularity helped cost Republicans control of Congress, Democrats have historically struggled to turn out their voters in midterm elections at the same rate as in presidential years, as Bill Clinton noted in Florida last week:

We're great at doing what's right if there's a presidential election on the ballot but we're not nearly as good as our Republican opponents are at showing up in the midterm elections."

The World

There's never a good time for the world to fall apart, but an election year is a particularly inconvenient time for the party in power. Voters may not directly blame congressional Democrats for the rise of the Islamic State, or Russia's aggression toward Ukraine, or the Ebola outbreak, but they have soured significantly on Obama's foreign policy, and that does not reflect well on his party's candidates.

It also contributes to a general sense that the nation is headed in the wrong direction, a mood that Republican candidates have tried to exploit in advertising.

At the same time, polls often show a rally-around-the-flag effect at times of crisis, which could lead to at least a temporary boost in support for Obama's foreign policy and his war with ISIS.

The Health Care Law

This factor would have been much higher on the list in late 2013, when the disastrous rollout of the Affordable Care Act threatened to unravel the core achievement of Obama's first term. Polls continue to show the law is unpopular, but it has faded to some degree as a top-priority issue, and Republicans are not focusing on it in ads to the same degree they did in 2010.

Yet the damage was done a year ago, in large part because the botched federal insurance website turned the nation's attention immediately away from the government shutdown that, for a few weeks, had Democrats thinking they could win back the House from Republicans this year. With the political attention span as short as ever, the GOP caught a big break as Democrats failed to seize on the political advantage they gained during the shutdown. Voters may not have completely forgotten that Republicans shuttered the government, but the Obamacare fiasco helped it fade more quickly from the headlines.

The GOP's Restraint

Todd Akin/AP

The Tea Party may have forced Republicans to shut down the government, but the GOP has been wiser about nominating the Tea Party's candidates in 2014. Republicans arguably could have won the Senate in 2012 if they had not fielded extreme or gaffe-prone candidates like Todd Akin in Missouri, Richard Mourdock in Indiana, or Sharron Angle two years earlier in Nevada. With the Republican establishment much more engaged in primary races this time around, Tea Party-backed candidates were turned aside in states like Georgia, Kentucky, and Mississippi, improving the party's chances of winning the Senate.

This article is from the archive of our partner The Wire.