Independent voters make up over 40 percent of registered voters in the United States today, while fewer than 30 percent are either registered Republicans or Democrats, and these voters will be the key to winning in swing districts without a partisan stronghold.

"Over the last 25 years, control of the House has flipped three times, and the party that won independents was the party that captured the majority. In 1994, Republicans wrested control by achieving a 14-percentage-point advantage among these voters. In 2006, Democrats won independents by 18 points and took over the House. The tables turned again in 2010 when Republicans won independent voters by 19 points, according to research by Dave Winston, a Republican strategist. 'The difference between a GOP victory and a GOP loss wasn’t base turnout,' he said. 'It was Republicans’ ability or inability to win independents.'"-Adele Malpass, RealClearPolitics

With only days left before the midterm elections, the New York Times recently introduced its readers to Kristen Donnelly, 35, an educated, affluent, suburban businesswoman living in Pennsylvania’s closely contested first district, just north of Philadelphia– and an independent voter.

She's exactly the kind of voter that Democrats are counting on to fuel a Blue Wave in the midterm elections, but although she "would never vote for Trump," she says she'll be voting for Rep. Brian Fitzpatrick, the Republican who's been leading the race by a hair:

"Lost in all the talk about a Democratic blue wave is a set of sober reality checks — from the quantifiable to the emotional — that may help Republicans reduce their losses, and possibly even retain their 23-seat majority.

In many neighborhoods with key House races, daily life is pretty good. Unemployment is at a five-decade low. Confidence is spilling over among consumers and businesses. The economy is on track to grow at its fastest pace in years."

California Will Be Key

California will be key to control of the U.S. House because of the size of its delegation. Nearly a third of the seats Democrats will need in order to flip the House are in the Golden State.

But early mail in ballot results in red districts like CA-45 where Democratic challengers are hoping to prevail reportedly show a red wave of strong early Republican voter turnout keeping pace with votes for the Democrat, despite polling that has suggested otherwise.

So in these districts it will be independent voters who decide the eventual outcome, not the hoped-for blue wave.

Statewide Elections

But it's not just the U.S. House results that will swing red or blue depending on which way independent voters swing this election.

Statewide election outcomes are also in the hands of independent voters this year. In Florida independents will decide the outcome of the U.S. Senate and governor's race.

In South Dakota the parties have scrambled to court the vote of an unaffiliated voting bloc that's grown by 70% since 2006.

And in a historic (and historically close) U.S. Senate race in Arizona, independents will choose the ultimate winner.