Here's more on the poll, from Yahoo News:

A month after Joe Biden was attacked by Sen. Kamala Harris over his record on race at the first Democratic presidential debate, the former vice president appears to have steadied himself, according to new polling released this week. And one national poll, released by Fox News, appears to have gotten under President Trump’s skin.

According to CNN’s poll of polls, which averages the results of the most recent national surveys, Biden (30 percent) has opened up a wide lead over Sens. Elizabeth Warren (16 percent), Bernie Sanders (14 percent) and Harris (12 percent), who has slipped back to fourth place from second. The California senator shot up to 17 percent in the same poll immediately following the first debate, then trailing Biden by just 8 points. She now trails him by 18.

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More encouraging for Team Biden is his lead in South Carolina, a state in which Harris has campaigned extensively. According to a Monmouth University survey of likely Democratic primary voters conducted earlier this week, Biden (39 percent) holds a commanding advantage over Harris (12 percent), who is followed by Sanders (10 percent) and Warren (9 percent). Notably, Biden has retained his strength among African-American voters, even over Harris, who is African-American: He leads there with 51 percent over Harris, at 12 percent.

And according to a Quinnipiac University poll released this week, Biden (50 percent) is the only candidate in the Democratic field who has more support than Trump (42 percent) among voters in Ohio. Trump has a 1-point edge (46 percent to 45 percent) over Sanders and Warren in Ohio in those theoretical general election matchups, while he is tied with Harris there.

Biden also has the edge over Trump in Florida (50 percent to 41 percent), Pennsylvania (53 percent to 42 percent) and even Texas (48 percent to 44 percent), Quinnipiac found.

But the poll that caught Trump’s attention was this one.

According to a Fox News survey released Thursday, Biden leads the president by 10 points (49 percent to 39 percent) among registered voters. Sanders holds a 6-point advantage over Trump (46 percent to 40 percent), but that’s within the poll’s plus-or-minus 3-point margin of error.

Trump predictably took the results in stride, with the philosophical calm with which he treats all bad news.

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"[email protected] is at it again," Trump tweeted. "So different from what they used to be during the 2016 Primaries, & before — Proud Warriors! Now new Fox Polls, which have always been terrible to me (they had me losing BIG to Crooked Hillary), have me down to Sleepy Joe.”

“Even considering the fact that I have gone through a three year vicious Witch Hunt, perpetrated by the Lamestream Media in Collusion with Crooked and the Democrat Party, there can be NO WAY, with the greatest Economy in U.S. history, that I can be losing to the Sleepy One,” the president added. “KEEP AMERICA GREAT!"