The most important thing to remember about the 2014 election, by @DavidOAtkins

If you want to understand the 2014 midterm elections, remember this simple fact about American politics: There just aren’t that many swing voters.

Many people change their minds over the course of a campaign about whether to vote and even which candidate they’re leaning toward. Ultimately, though, voters tend to come home to their favored party. There are relatively few voters who cross back and forth between the parties during a campaign or even between elections.

Political professionals have increasingly come to appreciate this pattern and have focused resources on getting previous voters to the polls. Both parties have spent considerable effort in recent elections trying to understand the effects of television ads, canvassing, phone calls and mailings on turnout. Mobilizing a party’s voters has become as important as persuading undecided or swing voters.

The 2010 midterm elections highlight the relatively small number of swing voters. After winning with a wide margin and extraordinary enthusiasm in 2008, the Democrats suffered one of the largest losses of seats in any midterm two years later.

Although the president’s party almost always loses seats in midterm elections, the size of the 2010 “shellacking,” to borrow President Obama’s description, created the impression that many voters had changed their minds about the president, his policy goals or his ability to get the country back on the right track between 2008 and 2010.

But only a small percentage of voters actually switched sides between 2008 and 2010. Moreover, there were almost as many John McCain voters who voted for a Democratic House candidate in 2010 as there were Obama voters who shifted the other way. That may be a surprise to some, but it comes from one of the largest longitudinal study of voters, YouGov’s Cooperative Campaign Analysis Project (C.C.A.P.), for which YouGov interviewed 45,000 people at multiple points during 2011 and 2012.

The results clearly show that voters in 2010 did not abandon the Democrats for the other side, but they did forsake the party in another important way: Many stayed home.

Fewer than 6 percent of 2008 voters in the presidential election voted for a congressional candidate from the other party in 2010, with the switchers roughly evenly divided across the parties, according to the C.C.A.P. It’s worth noting, however, that these switchers are not evenly distributed around the country, with North Dakota’s single district having very few cross-party voters (under 3 percent) and some Pennsylvania districts, for example, having upward of 10 percent switching between 2008 and 2010.

On average, across districts, roughly 6 percent of Obama voters switched and just under 6 percent of McCain voters switched; because there were more Obama voters than McCain voters in 2008, this means — as you’d expect — that more voters swung to the Republicans than to the Democrats. An additional 1.5 percent switched to third-party candidates.

But on turnout, the numbers were not evenly balanced for Democrats and Republicans. Only 65 percent of Obama’s 2008 supporters stuck with the party in 2010 and voted for a Democrat in the House. The remaining 28 percent of Mr. Obama’s voters took the midterm election off. By comparison, only 17 percent of McCain’s voters from 2008 sat out the midterms.

Ventura County Democrats, on the other hand, don’t feel they need to change their message to attract independent voters.

“The majority of all voters agree with our position on social and economic issues,” said David Atkins, chair of the Ventura County Democratic Party. “If we get our message out about our issues and about what we stand for, the majority of voters will agree with us and select our candidates. It’s not a question of working harder to appeal to another kind of voter. We just have to make sure that the majority of people who agree with us get out to vote.”

In an assessment different from the Gallup report’s findings, Atkins said it’s a common misconception that independent voters are undecided or have more moderate views.

“Independent voters are simply people who have made a choice not to register with the party, but they’re just as liberal or conservative as their counterparts, often more so,” Atkins said.

He said registering as an independent is a cultural trend, especially popular among young people. But younger voters are still progressive on most issues, including immigration reform, reproductive rights and America’s growing wealth disparity.