A recent Washington Post poll highlights the Achilles’ heel of Donald Trump's campaign: Minority voters, namely blacks and Hispanics, don't support him.

The poll, released Wednesday, only shows the problem is evolving for the presumptive Republican presidential nominee. A staggering 94 percent of black adults surveyed view Trump negatively, a 13 percent increase since the same poll was conducted in May.

While Trump's likely general election opponent, Democrat Hillary Clinton, is boasting a 79 percent favorability rating among black Americans, Trump is fighting claims of racism after launching attacks on a U.S.-born judge of Mexican descent.

"I am not a racist, in fact, I am the least racist person that you've ever encountered," Trump said to The Washington Post last week, defending his comments that U.S. District Judge Gonzalo Curiel's Mexican heritage creates a conflict of interest that prevents him from fairly presiding over a case involving Trump University.

Those comments were met with scorn by both Democrats and Republicans, with Speaker Paul Ryan (R-Wis.) calling it "textbook" racism.

Trump's campaign has been frequently marked by stumbles while trying to court minority voters.

His policy stance of barring Muslim immigrants from entering the U.S. "temporarily,” until the government can "figure out what is going on,” has been generally opposed by Republicans. 

And his vow to build a wall between the U.S. and Mexico hasn't helped his unpopularity among Hispanic voters.

The Post's poll showed 89 percent of Hispanic-Americans surveyed view Trump unfavorably, a 5 percent increase from May.

It's an issue the Republican National Committee (RNC) recognizes as it invests more resources into reaching out to minority voters.

"My prediction is we're going to get a higher percentage of the Hispanics and black vote than we have gotten since 2004," RNC Chairman Reince Priebus said in an interview with Bloomberg Businessweek in May.

"And we're going to do it because we've done a better job at the RNC, and we're also going to have a nominee who is going to pivot in tone and tenor. He understands that."

Trump maintains he will do well among minority voters come November, saying his message of bringing back jobs to the U.S. resonates with the demographic that typically sees higher levels of unemployment.

"I'm going to do great with the African-Americans. African-American youth is 58 percent unemployed. African-Americans in their prime are substantially worse off, you know, economically than a — than the whites in their prime. And it's very — it's a very sad situation," Trump said on CNN in February.

The poll was conducted among 1,000 adults June 8–12 and has a margin of error of 3.5 percentage points.