Swing the election?

Could undecided voters swing the election?

They tend to be young, admiring of Bernie, and deeply dissatisfied with Clinton and Trump. But no one knows if they're persuadable.

By Steven Shepard

They tend to be more younger than older.

They are less likely to identify with either of the two parties.

And they strongly dislike both major-party candidates.

They are 2016’s undecided voters — or at least those who tell pollsters they won’t choose between Donald Trump and Hillary Clinton. Sometimes they say they won’t vote for either candidate. Other times, they say they will vote for another candidate when offered only Trump and Clinton, or they will choose Gary Johnson or Jill Stein when pollsters prompt with those names. Or sometimes they say they won’t vote at all.

Even as Clinton builds a consistent lead in the weeks following the national party conventions, this bloc of voters — which usually ranges between 8 and 20 percent of voters — could still tip the scales in November.

While most pollsters insist it's too early to predict which candidate is likely to win undecided voters over, Clinton would appear to have the most to gain or lose: They're more likely to come from a demographic — younger voters — that's more inclined to back her, and in some surveys have a slightly less negative view of her than of Trump. And yet they've resisted supporting her all year, and are actively seeking other options, such as Johnson or Stein.

"I don't think it's locked in," said John Della Volpe, the director of polling at the Harvard Institute of Politics and an expert on younger voters. "It's not even September yet."

A POLITICO review of polling data — both publicly released and shared from unreleased crosstabs — establishes a profile of those neither-Trump-nor-Clinton voters: primarily independent, younger and strongly aligned against both politicians.

It’s hardly unusual for voters who identify as independents to say they are undecided in a presidential election. But what is uncommon about 2016 is that these voters have overwhelmingly negative opinions about both candidates — suggesting it will be difficult for either to bring those voters into the fold.

The latest round of national polls, conducted in late July or August, after the conventions, paints a reliable picture of the voters either on the fence or firmly aligned against both major-party candidates. The sample sizes of undecideds in each poll are small, but some patterns are apparent across most of the polls:

Republicans are slightly more diffident about Trump than Democrats are about Clinton. But those who don’t identify with one of the two parties are significantly more likely to be undecided.

In a Fox News poll of registered voters, conducted July 31-August 2, only 8 percent of self-identified Democrats said they preferred another candidate, wouldn’t vote or were undecided. A modestly higher percentage of Republicans, 10 percent, were undecided. But fully a quarter of independents said they were undecided.

An ABC News/Washington Post poll, conducted August 1-4, showed fewer undecided voters overall, but the same pattern: 3 percent of Democrats, 6 percent of Republicans and 12 percent of independents couldn’t choose between the candidates.

The late-July CBS News poll was similar: 4 percent of Democrats, 6 percent of Republicans and 22 percent of independents said they supported another candidate, wouldn’t vote, or said their choice depends on other factors or were undecided. Put another way: 73 percent of those who didn’t make a choice identify as independents, 16 percent were Republicans and 11 percent were Democrats.

It all comes at a time when more voters are self-identifying as independents, according to University of Arizona professor Samara Klar, the co-author of a new book on independent voters.

That has implications not just in the number of independent voters who stay home on Election Day, but also those who do vote but are otherwise less engaged in the political process.

“When people are saying they are independent, they might be voting for their preferred party, but they’re not putting up a yard sign or putting on a sticker,” Klar said. “And those things matter.”

Younger voters are more likely to be undecided.

One-in-five voters under age 35 in the Fox News poll wouldn’t choose between the two candidates, compared to just 12 percent of voters aged 35-54, and only 9 percent of voters 55 and older. And in a subsequent, three-way matchup, 19 percent of voters under 35 said they would vote for Johnson, the former New Mexico governor running on the Libertarian Party line — far more than the 13 percent of voters aged 35-54 and the 6 percent of voters 55 and older.

In the two-way matchup in the CBS News poll, a majority of those undecided voters, 55 percent, were under the age of 45, even though the younger voters comprised just 39 percent of the 2012 electorate, according to the Census.

The independence of younger voters from both major parties isn’t new: 4 percent of voters under age 25 cast their ballots for candidates other than President Barack Obama or Mitt Romney four years ago, according to the exit polls — roughly double the national average.

But the impact on the presidential race is two-fold: Younger voters aren’t lining up with Clinton in the numbers they did for Obama in 2012 or 2008, cutting into her margin over Trump. And Trump’s struggles with young voters go even beyond Romney and John McCain, at a huge risk to the GOP’s future.

Della Volpe said younger voters are poised to be the 2016 cycle's latest deciders. He attributed part of the reticence among young voters to their fervent support for Sen. Bernie Sanders (I-Vt.) in the Democratic race. But he also cited data from a July survey showing that nearly twice as many voters aged 18-29 viewed Clinton unfavorably (60 percent) as had a favorable opinion of her (31 percent).

"Among young people, I think it’s a combination of the persistent halo of everything related to Sanders," Della Volpe said. "And Hillary’s favorable rating [among young voters] was two-to-one unfavorable before the convention."

Undecided voters don’t like either Clinton or Trump.

This is why it will be so difficult for either candidate to win over these voters. In the CBS News poll, the respondents who declined to pick Clinton or Trump were overwhelmingly aligned with both of them.

Among those undecided voters, only 5 percent said they had a favorable opinion of Clinton, according to data provided by CBS News’ polling unit. The majority, 54 percent, said they viewed Clinton unfavorably. (About a third said they were undecided or hadn’t heard enough about Clinton.)

Trump’s numbers were even worse. Only 3 percent of undecided voters said they have a favorable impression of the GOP presidential nominee, compared to 54 percent who had an unfavorable opinion.

The big question: Will these undecideds actually vote?

The undecided share of the electorate could be determinative if they lined up decisively behind one of the two candidates.

But it’s more likely that they won’t even vote in the presidential elections, pollsters said. Younger voters and those who identify as independents are less likely to vote than older voters and more committed partisans.

"Given what I’ve seen over the past year, it’s not surprising that young people are the last to decide if they’re going to vote, and whether they are going to vote for a particular candidate," Della Volpe said.

As the calendar moves past Labor Day, pollsters will begin testing for this, eliminating unlikely voters from their polls and only reporting results for those who will probably cast ballots in November.

That could serve to eliminate some of the demographic and attitudinal differences among undecided voters. The first major national poll of likely voters, a Quinnipiac University poll conducted August 16-24, found fewer undecided voters overall, and smaller differences by age: 7 percent of voters under 35, 8 percent of those 35-49, 7 percent of those 50-64 and 6 percent of voters over 65 were undecided in that survey.

On another ballot test question including Johnson and Stein, however, those age differences reappeared. More than a quarter of voters under age 35, 27 percent, said they would vote for Johnson and Stein, combined. But just 5 percent of voters 65 and older picked a third-party candidate.