CNN's data reporter is sounding the alarm on a "very troubling" sign for the Biden campaign: Donald Trump's support among black voters has more than doubled.

"Look, if you look at 2024, Biden still leads among black voters over Donald Trump, 69% in an average of polls," CNN's Harry Enten said. "But look at this number for Donald Trump: 22%. Where was Donald Trump at this point? Four years ago in the poll, he was just at 9% of the vote."

"So he's seen more than a doubling in his support among African-Americans," he continued. "This margin, which was in the 70s, just four years ago, look at where it is now — 69, minus 22. That puts it in the 40s. My goodness gracious."

"If this held through the general election, obviously we're still months away, this would be by far the best performance for a Republican candidate among black voters in a generation, two generations, probably since 1960 and Richard Nixon against John F. Kennedy," he went on. "That's how long we're really talking about."

"This could be a truly historic margin," he added. "It's quite a troubling sign for the Biden campaign."

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But the polling data gets even worse for Biden when factoring in age: Young black voters are even more strongly disposed to lean towards Trump.

While Biden gets support from 82 percent of black voters over age 50, his support drops to just 62 percent for those under 50. Trump's support for black voters ages 18 to 49 is one in four voters or 25 percent.

"Who are these voters?" he asked. "And let's break it down by age, because I really think this gives you a good insight into what's exactly cooking here. Take a look here. If you look among black voters, age 50 and over, you see that Joe Biden has a very substantial lead. Look at this: 82% to 8%. This lead is still in the 70s. This looks a lot like what we saw in the overall polling back in 2020."

"But look at voters under the age of 50. Look here, Donald Trump is pulling 25% of that vote. Joe Biden, is at just 62% of this vote. This lead, Sarah, this lead is just south of 40 percentage points. This is historic."

"This is what a lot of folks have been talking about, that Joe Biden has a specific problem among younger black voters, and that is exactly what's showing up right here. And this is, I think, a lot of the reason why you're going to see Biden focusing more on black voters, why you're seeing Jim Clyburn go out there," Enten said.

"Don't be surprised if they go to more colleges, because the fact of the matter is older black voters still really much like Joe Biden," he continued. "It's these younger black voters who very much are turning on him and being much more supportive of Donald Trump than they were four years ago."

This is exactly what NBC News found out when its reporter recently went out to Donald Trump's rally in the Bronx.