Former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE and Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) are statistically tied with President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE in Arizona, a state that hasn't voted for a Democratic presidential candidate in a quarter century, according to a new poll.

The new survey conducted by OH Predictive Insights, a Phoenix-based nonpartisan pollster, shows Biden leading Trump by a 45 percent to 43 percent margin. Trump leads Warren 44 percent to 43 percent, the poll found.

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Both results fall within the survey's margin of error, a sign that Trump will have to work harder to win Arizona's electoral votes than any Republican nominee this century.

The survey shows Trump running better against other potential Democratic nominees. He leads Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) 44 percent to 34 percent; he leads Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.) 45 percent to 36 percent; and he leads South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE (D) 43 percent to 38 percent.

Trump "is in the low- to mid-40s, which I'd say is a pretty big red flag," said Mike Noble, a Republican pollster and managing partner and chief of research at OH Predictive Insights. "He's not doing himself any favors for 2020 in a state he won in 2016."

In the group's last survey, conducted in May just after Biden entered the race, Trump led every Democratic candidate except Biden by a statistically significant margin. The May survey showed Biden leading Trump 49 percent to 44 percent.

Since that last survey, Noble said, Trump's approval ratings have sagged — and they have taken his head-to-head numbers against Democrats down with them. As a consequence, Trump now appears vulnerable in a state that has rarely been competitive at the presidential level.

Trump's approval rating stands at 47 percent among Arizona voters. Fifty-two percent say they disapprove.

Though there are about 145,000 more registered Republicans than Democrats in Arizona, independent voters there appear to be breaking against Trump. Just 38 percent of independents approve of Trump's job performance, and 60 percent disapprove.

Trump trails among independent voters against all five Democratic candidates the poll tested. Biden holds a wide 50 percent to 34 percent lead among those voters, and Warren leads Trump 45 percent to 35 percent.

In 2016, Trump won independent voters in Arizona by a 47 percent to 44 percent margin, according to exit polls.

In 2018, when Kyrsten Sinema became the first Democrat to win a U.S. Senate seat in Arizona since Dennis DeConcini won reelection in 1988, Sinema beat Republican Martha McSally Martha Elizabeth McSallyOn The Trail: Making sense of this week's polling tsunami The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE among independents by a slim 50 percent to 47 percent margin.

No Democratic presidential nominee has won Arizona's electoral votes since 1996, when Bill Clinton William (Bill) Jefferson ClintonHarris: Ginsburg 'absolutely' cleared the path for me Anxious Democrats amp up pressure for vote on COVID-19 aid Barr's Russia investigator has put some focus on Clinton Foundation: report MORE beat Bob Dole by about 2 percentage points and Reform Party nominee Ross Perot took 8 percent of the vote.

But Hillary Clinton Hillary Diane Rodham ClintonBloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE came closer than anyone since her husband. Trump won just 48.7 percent of the vote in Arizona in 2016, edging Clinton's 45.1 percent. The Clinton campaign spent a small amount of money to make a play for Arizona's electoral votes.

The poll shows signs, too, that favoring gun control or gun safety legislation is no longer a negative in a state known for its libertarian leanings. The poll found 56 percent of Arizona voters would be more likely to vote for a candidate who favors gun safety legislation. Only 19 percent said they would be less likely to support such a candidate.

Nearly two in three voters, 64 percent, said they somewhat or strongly support banning assault-style weapons. Sixty-two percent said they support banning high-capacity ammunition magazines. A whopping 84 percent said they support so-called red flag laws, which allow law enforcement officials to take firearms away from someone who poses a danger to themselves or others. And 83 percent said they would support raising the minimum age to purchase a firearm to 21 years old.

The eventual Democratic presidential nominee will be running alongside Mark Kelly, the retired astronaut and husband of former Rep. Gabrielle Giffords (D) who is running for the U.S. Senate seat McSally now holds. The same OH Predictive Insights poll showed Kelly leading McSally, 46 percent to 41 percent.

The survey polled 600 likely Arizona voters Aug. 13–14. It carried a margin of error of plus or minus 4 percentage points.