2016 Trump's other polling headache Hillary Clinton's convention bounce isn't the only thing the GOP nominee should be worried about.

Another traditional Republican advantage may be going by the wayside this year: Donald Trump, falling perilously behind Hillary Clinton in the polls, isn’t getting the standard “likely voter” bump that usually boosts GOP candidates in the closing weeks of the election.

Every four years around Labor Day, the major national pollsters begin an effort to discern which voters will actually show up at the polls and cast ballots in the presidential race. And when the polls switch from measuring the preferences of all registered voters to those most likely to turn out — a smaller pool of voters — it typically results in improved standing for the GOP candidate.


That’s because established Republican constituencies — namely older voters, but also sometimes whites, wealthier and more educated voters — turn out at higher rates than some core Democratic demographic groups, like younger voters. According to the Census’ Current Population Survey, only 45 percent of U.S. citizens aged 18 to 29 cast ballots in 2012, compared with 68 percent of those 45 to 64, and 72 percent of senior citizens 65 and older.

But while the switch to likely voters in public polling is just beginning, all indications are that Trump won’t run better among the voters who will actually turn out this fall, compared with the universe of all Americans on the voting rolls.

That could be due, in part, to Trump’s reliance on less-traditional voters who haven’t been regular participants in the presidential elections. But that explanation seems unlikely: Most of Trump’s primary and caucus supporters have already been general-election voters. And polls weren’t missing those Trump supporters, anyway: The New York real-estate magnate didn’t out-perform his polling numbers in the primaries.

What’s more likely happening is that Trump — viewed unfavorably by nearly two-thirds of voters — isn’t motivating enough Republican or Republican-leaning voters the way previous GOP nominees have. Polls show Clinton supporters and Democratic voters are as enthusiastic about participating in the general election as Trump backers and Republicans — if not more so.

That’s a big turnaround from four years ago, when despite President Barack Obama’s overall advantage among the electorate, Republicans and voters who said they supported former Massachusetts Gov. Mitt Romney were the more enthusiastic and motivated group.

That phenomenon was clearly on display when a number of national pollsters began screening for likely voters in August and September 2012. Obama’s registered-voter lead over Romney immediately shrank among likely voters in all seven major national polls the first time they implemented a likely voter screen.

The movement among likely voters was occasionally jarring. Over the seven polls, Obama’s margin over Romney shrank by more than 4.4 points. A CNN/ORC poll in late August 2012 found Obama leading Romney by 9 points among registered voters, but only 2 points among likely voters. After the conventions that year, in early September, Obama’s 6-point lead among registered voters in an ABC News/Washington Post poll was slashed to just a point.

While only a handful of national public polls have started surveying likely voters, that doesn’t seem to be happening this year. Clinton led Trump by 8 points among registered voters in the ABC News/Washington Post poll released on Sunday, and 7 points among likely voters. A Monmouth University poll out Monday moved slightly in the other direction: Clinton led by 12 points among registered voters and 13 points among likely voters. (The new Bloomberg News likely-voter poll did not produce results for all registered voters.)

Patrick Murray, director of the Monmouth University Polling Institute, said Trump’s numbers among likely voters are unlikely to grow until Republicans are motivated to start telling pollsters they will cast ballots. In Monmouth’s new poll, Murray said, 79 percent of Democratic voters said they were certain to vote, compared with only 61 percent of GOP voters.

“For one thing, [Trump is] not a Republican,” Murray said, when asked why Republicans are saying they aren’t certain to vote. “As we’ve seen particularly over the past couple of weeks, most voters feel that he’s temperamentally unfit for office, and that’s being reinforced by leaders of their own party.”

Likely voter screens and other similar measures at the state level aren’t helping Trump, either. In two of the three NBC News/Wall Street Journal/Marist state-level surveys released Tuesday — polls in Iowa, Ohio and Pennsylvania — Clinton’s lead actually grew among those voters who said they would definitely turn out in the fall. (Marist’s official likely voter screen, which the school will unveil next month, differs somewhat from a simple vote-intention question.)

Marist College pollster Lee Miringoff credits Clinton’s performance among more-certain voters to a growing education gap: Even among white voters, Clinton has more support among the college-educated, while Trump runs better with voters who didn’t attend college. And more-educated voters, historically, vote at higher rates than less-educated voters.

“She’s doing better among white, college-educated voters, and he’s doing better among white non-college voters,” Miringoff said. “The fact that the Democrat is doing better among white college [voters], that’s unusual. And they tend to vote.”

The Marquette Law School Wisconsin poll — which uses the vote-intention question as a likely voter screen — released Wednesday found Clinton leading by 10 points among all registered voters. But that lead swelled to 15 points among likely voters.

Marquette pollster Charles Franklin said that the advantage has shifted between the candidates during the course of the general-election campaign.

“We’ve seen some fluctuation in this,” Franklin said. Leading up to the closely watched GOP presidential primary in April, “Republicans had the usual 5- or 6-point advantage in turnout among likely voters vis-à-vis Democrats.” Clinton then grabbed the likely voter advantage in Marquette’s June poll as she surged nationally, but Trump snatched it back in July.

Franklin pointed to Trump’s relative performance among Republicans — he’s winning just under 80 percent of self-identified Republican voters in the Marquette poll — calling it the result “of a more divided Republican Party that the convention did not substantially ameliorate. And that’s affecting the turnout likelihood, but it’s also at this point not bringing home those reluctant Republicans not yet ready to vote for Trump.”

What’s most troubling for Republicans is that voters’ ambivalence about Trump could hurt their candidates down the ballot. In the NBC News/Wall Street Journal/Marist polls, Democratic Senate challengers each gained on their incumbent GOP opponents when only those who said they were certain to vote were measured. In Iowa, former Lt. Gov. Patty Judge slashed her deficit against Sen. Chuck Grassley from 10 points to only 1 point among self-described certain voters.

In the Marquette poll, former Democratic Sen. Russ Feingold’s 6-point lead over incumbent GOP Sen. Ron Johnson among Wisconsin registered voters became an 11-point advantage among likely voters. Franklin, the Marquette pollster, said Johnson can try to distance himself from Trump and win some soft Clinton supporters — and there are signs it’s working to some degree, given his deficit in the polls is smaller than Trump’s.

But Johnson and other down-ballot GOP candidates “can’t avoid the problem of Republicans not turning out,” Franklin said. “He still has to face a likely -voter electorate which has relatively speaking fewer Republicans than we might see in other election years.”