Former Vice President Joe Biden Joe BidenOmar fires back at Trump over rally remarks: 'This is my country' Trump mocks Biden appearance, mask use ahead of first debate Trump attacks Omar for criticizing US: 'How did you do where you came from?' MORE topped President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE by 9 percentage points in a Fox News poll released on Saturday.

The likely Democratic nominee was backed by 49 percent of the survey's respondents in a theoretical matchup against Trump, who had 40 percent support. An additional 11 percent said they are undecided or will vote for someone else.

Last month, Biden had an 8-point lead over Trump, at 49 to 41 percent.

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The former vice president in the new poll has a 9-point lead over Trump among voters who are extremely interested in the election, 52 to 43 percent. Biden also holds an 8-point advantage in battleground states, 48 to 40 percent.

But in counties where former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE and Trump were within 10 points of each other in 2016, Biden has a 25-point advantage, 57 to 32 percent.

When the theoretical matchup included Biden’s potential vice presidential candidate, only Sen. Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (D-Mass.) tipped the Democratic ticket to majority support at 52 percent, compared to the Trump ticket at 42 percent.

Sen. Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (D-Calif.) or Sen. Amy Klobuchar Amy KlobucharSocial media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D-Minn.) both push the Biden ticket to 50 percent, while Trump’s ticket stays at 42 percent.

Biden has committed to choosing a woman as his vice presidential candidate.

The Fox News poll of 1,011 randomly chosen registered voters was conducted between March 21 and 24. It has a margin of error of 3 percentage points.