Two states further into the primary calendar, Georgia and Louisiana, have postponed their primaries over the outbreak of coronavirus. But the disease is expected to have less impact on turnout in Arizona than in other states, thanks to the state's extensive mail balloting program, even though Arizona's largest county - Maricopa, home to a majority of the state's voters - is closing many polling places because of the virus.
Among those who said they have already cast their ballots, Biden leads by 33 points, 50 percent to 27 percent.
"Biden has a strong advantage going into the primary. This is because much of his support has already been banked in the early vote," Monmouth University pollster Patrick Murray said in a news release announcing the poll results. "The closure of many polling places due to COVID-19 means it is uncertain how many voters who planned to vote on Tuesday will actually show up."
Biden's biggest leads come among older voters - he leads Sanders, 75 percent to 8 percent, among those 65 and older - and white voters, 55 percent to 26 percent. Sanders, on the other hand, leads Biden by a 2-to-1 margin, 56 percent to 28 percent, among voters younger than 30. And Sanders has a slight lead over Biden among Latino voters, 48 percent to 41 percent.
The Monmouth survey was only conducted in English, but the results for Latino voters closely match other surveys that included Spanish-language interviews, including polls for Univision Noticias/Arizona State University and Noticiero Telemundo.
A majority of Democratic primary voters, 63 percent, say it's more important to pick a nominee to defeat President Donald Trump than the address their own top policy issue.
As for the general election, the poll shows Arizona - which Trump carried by 4 percentage points in 2016 - is a burgeoning battleground state.
The Monmouth survey shows Arizona starting the 2020 general election as a toss-up with either Democrat at the top of the ticket, though Biden leads Trump by 3 points, 46 percent to 43 percent, while Trump holds a scant, 1-point lead over Sanders, 44 percent to 43 percent.
Democrats also have an advantage in the state's closely watched special election for Senate. Retired astronaut Mark Kelly leads appointed GOP Sen. Martha McSally, 50 percent to 44 percent. While Kelly, the husband of former Rep. Gabrielle Giffords (D-Ariz.), has never run for public office, his personal favorability rating (41 percent favorable, versus 17 percent unfavorable) exceeds McSally's (35 percent favorable, versus 39 percent unfavorable). McSally aired early attack ads against Kelly on TV this year trying to tag him as a partisan Democrat and tie him to the most liberal elements of the party.
The poll was conducted March 11-14, beginning the day Trump addressed the nation on the coronavirus crisis and continuing for three more days of fast-breaking developments that have culminated in the partial shutdown of American life. It was conducted entirely prior to Sunday's Democratic debate, which had been planned for Phoenix but was moved to Washington amid concerns about coronavirus.
Among Arizona voters, 21 percent say they are "very concerned" about someone in their family becoming seriously ill from the coronavirus, and an additional 32 percent said they were "somewhat concerned." But a significant share of voters said they were "not too concerned" (28 percent) or "not at all concerned" (19 percent).
Democrats were far more concerned about coronavirus than Republicans were: A combined 75 percent of Democrats said they are very or somewhat concerned, compared with 41 percent of Republicans. The majority of Republicans, 58 percent, said they were not too concerned or not concerned at all.
Voters in Arizona are split on Trump's handling of the outbreak. A combined 49 percent said he's doing a "very" or "somewhat good" job, while 46 percent said he's doing a "very" or "somewhat bad" job.
The poll surveyed 847 registered voters and has margin of error of plus or minus 3.4 percentage points. For the subsample of 373 likely Democratic primary voters, the margin of error is plus or minus 5.1 percentage points.