Donald Trump has run head-first into an electoral wall.

In poll after poll, Trump isn't even close to winning a majority of the vote. While he’s narrowed the gap between his campaign and Hillary Clinton in recent weeks, in the past 21 national polls conducted using conventional phone or internet methodologies over the last five weeks, Trump’s high-water mark in a head-to-head matchup with Clinton is 44 percent.


And when third-party candidates — Libertarian Gary Johnson and Green Party nominee Jill Stein — are included, Trump’s highest poll score is only 40 percent, well below Clinton’s high of 50 percent.

The GOP presidential nominee’s limited support isn’t necessarily prohibitive for his chances — especially if Johnson and Stein continue to draw, combined, more than 10 percent of the vote. He only trails Clinton by 4 percentage points in the RealClearPolitics average and by 5 points in the HuffPost Pollster model. But if support for the third-party candidates dwindles closer to Election Day, Trump’s inability to expand his base could tilt the race further toward Clinton or require him to find a way to win with only a plurality of the vote, rather than a majority.

The national polls are striking, even with Trump drawing closer to Clinton in recent weeks. Of the 21 surveys that tested just Trump and Clinton, the Republican failed to break 40 percent four times. In most of the polls — 12 out of 21 — Trump was at either 41 or 42 percent.

Only two polls showed Trump hitting 44 percent: a Bloomberg News phone poll in early August that had Clinton leading by 6 points, and an Economist-YouGov web survey later in the month that showed Clinton ahead by 3 points.

Clinton, meanwhile, earned 50 percent or greater in 6 of the 21 polls.

The numbers aren’t much better for Trump in the four-way matchups with Johnson and Stein. In those 28 polls conducted since the beginning of August, Trump only hit the 40-percent mark four times — three of them automated-phone surveys from Rasmussen Reports, which has a consistent and heavy Republican lean.

Overall, Trump was at 37 percent or under in half of the 28 four-way surveys. Clinton, meanwhile, topped out at 50 percent in a Monmouth University survey last month. But, more recently, she has mostly been in the low-40s in ballot-test questions including Johnson and Stein.

The battleground-state polls also point to a low Trump ceiling. He currently trails in all 11 states that comprise POLITICO’s Battleground States project . And in the 54 polls across those 11 states that make up the polling average, he’s only broken 45 percent three times: He was at 45 percent in Quinnipiac University polls conducted in late July and early August in Florida and Ohio, and he was at 47 percent in a CNN/ORC poll in North Carolina last month.

But even despite those higher numbers, Trump trailed Clinton in all three of those polls, albeit only narrowly.

(A note on methodology: The national polls used in POLITICO’s analysis were compiled from RealClearPolitics, including all surveys conducted beginning on August 1, with a couple of exceptions. The Los Angeles Times/University of Southern California tracking poll — which has showed better results for Trump than other polls — was excluded since it re-interviews the same respondents repeatedly over time, and because it uses self-reported 2012 vote as a fixed weight. And polls by Gravis Marketing — from which the Trump-friendly website Breitbart News is also commissioning surveys — are also excluded, since Gravis eschews undecided voters in some of their releases .)

During the GOP primaries, Trump’s critics frequently pointed to what they said was his ceiling among Republican voters. But while there were times during the primaries when his support leveled out , Trump's path to the nomination consisted of a number of surges that ultimately ended with the real-estate magnate being the choice of a majority of GOP voters nationwide.

The general election, thus far, has been markedly different. Clinton has led Trump consistently, with just a few exceptions. And even though recent weeks show a slight uptick in Trump's numbers, there's no similar long-term trend that suggests he is poised to hit new highs in support among all general-election voters in the coming weeks.

With just two months left in the campaign, that leaves Trump with a tall task to break through his ceiling: He needs to convince more voters who don’t like him to vote for him.

According to HuffPost Pollster, Trump’s average unfavorable rating is 58 percent — a number that closely resembles the percentage of voters who don’t choose him in general-election matchups. (Trump’s average score in two-way polls with Clinton is 42.1 percent, according to RealClearPolitics.)

Clinton isn’t popular, either: Her unfavorables are nearly as high as Trump’s, with her average unfavorable rating sitting at 55 percent. (Clinton is at 46 percent in a two-way ballot test, per the RealClearPolitics average.)

Another reason Trump’s support is limited, compared to Clinton? In matchups with her — even without the third-party candidates — he is winning fewer Republicans than she is winning Democrats.

Trump is winning under 82 percent of Republicans in an average of the seven most-recent head-to-head polls that provided results by political party. Clinton, meanwhile, is winning nearly 85 percent of self-identified Democrats.

The voters who identify with each party but aren't yet supporting that party's standard-bearer are higher than in previous elections. But each candidate faces obstacles in bringing those voters home — specifically, those voters' perceptions of the candidates' images.

For now, Trump’s gains are as much a result as a slight uptick in his support as a decline in Clinton’s from her post-convention high. One month ago, on August 6, Clinton led Trump by 8.3 points, 48.1 percent to 39.8 percent, according to HuffPost Pollster.

Today, Clinton’s lead has shrunk to 5.4 points: 47 percent to 41.6 percent. Clinton has lost a little over a point since Aug. 6, while Trump has gained a little under 2 points. (RealClearPolitics shows similar numbers: Clinton has lost 1.2 points, while Trump has gained 1.7 points.)

Neither candidate has much more room to grow, however, despite less-than-stellar numbers among their own partisans. A Fox News poll released last week — which found Clinton leading Trump by 6 points, 48 percent to 42 percent, in a head-to-head matchup — asked follow-up questions to respondents after the ballot test that explore what a Trump ceiling could look like on Election Day: If you weren’t supporting Clinton or Trump, they asked, would you ever consider it?

Only 13 percent of those not backing Trump (which made up 58 percent of all respondents) said they could imagine voting for him, while 85 percent said they would never even consider it. Even allocating those who aren’t currently backing Trump but can imagine doing so under some circumstances, that puts the GOP nominee between 49 and 50 percent of the vote.

Clinton isn’t on pace to win a broad mandate if she prevails on November 8: Just 13 percent of the 52 percent not backing her said they could consider doing so. But that vaults her potential ceiling to just under 55 percent, about 5 points clear of Trump’s.

With nine weeks until Election Day, Trump will have opportunities to reset voters’ perceptions of him — especially with three nationally televised debates on the calendar. But with a ceiling currently between 40 and 44 percent, he’s at a distinct disadvantage against Clinton. And in order to claim a majority of the vote on Election Day, polls indicate he will have to win over voters who right now say they have decided they can’t ever vote for him.