TUCSON, Ariz. (CN) — Coming off a string of losses across the South and Midwest, Vermont Senator Bernie Sanders faces an uphill battle in Arizona Democrats’ presidential primary Tuesday.

Polls, nationally and in Arizona, show former Vice President Joe Biden with a sizable lead over Sanders, leaving the famously gruff and persistent senator scrambling to pull together enough delegates to carry the party’s flag to the convention and the White House.

Ultimately, the Arizona primary is about President Donald Trump, said University of Arizona political science professor Tom Volgy.

“Historically, people tend to vote (in primaries) for or against whoever is in the White House,” Volgy said.

A Reuters/Ipsos poll released Monday had Biden leading Sanders 59% to 41% in a head-to-head matchup among Democratic voters nationally and 55% to 45% when the sample included independents — who account for about one-third of Arizona voters. Tulsi Gabbard, the only other Democrat in the race, registered 3% support in the poll taken in the days after Super Tuesday.

About half of the Sanders supporters in the poll (51%) said they would vote for Biden in the general election if he is the party’s nominee, while 12% would vote for a third party, 8% for Trump and 28% were unsure or would not vote.

Volgy thinks this year’s Arizona’s primary will be different from 2016, when more voters followed their hearts. In 2016, few Democrats thought Trump had a chance to win against any viable Democrat, so they voted their conscience in the primary.

This year, he said, they are more likely to get behind a second choice if they think he can win. Having a two-man race makes that choice less complicated, Volgy said.

“My guess is that it is going to help Biden,” he said.

Sixty-seven convention delegates are at stake in Arizona, where the nominee will vie for 11 Electoral College votes. Arizona has a closed primary, meaning that only registered party members can vote.

Citizens registered as independent must register with a party to vote. The Arizona Republican Party shelved its primary, opting to give all its delegates to Trump.

An Arizona poll published Monday by the Phoenix research firm OH Predictive Insights shows Biden with a virtual lock on the election among likely Democratic voters. In the telephone poll conducted March 3-4, 45% said they support Biden, while just 17% back Sanders, a crushing lead that easily clears the poll’s 4.9% margin of error.

Biden held a similar lead among men, women, rural, white and Hispanic voters. Sanders’ only lead over Biden in the survey — a statistical tie — was among voters younger than 54, where the Vermont senator garnered 30% to Biden’s 29%.

Volgy does not think health care — consistently among voters’ top issues this year in 2020 — is a dividing issue in Arizona, as it was in Nevada, where the powerful Culinary Union kept the issue at the forefront.

People increasingly like the Affordable Care Act, and Sanders’ Medicare for All plan could threaten it, but so long as both candidates bring a strong message that they want everyone to have affordable, effective coverage, Volgy calls that issue “a wash.”

FiveThirtyEight, an ABC News polling project, showed Biden leading Sanders 52% to 35% in national polls. Just two weeks ago the poll had Sanders leading Biden 28% to 15%.

Whoever earns the Democratic nomination in July has an influential ally in Arizona, where former New York City Mayor Michael Bloomberg’s campaign hired 50 people to staff four offices. Bloomberg, who spent roughly $500 million on his own bid for the nomination, dropped out of the race March 4 and quickly endorsed Biden.

The billionaire communications industry magnate has vowed to keep his campaign alive in battleground states, including Arizona, for the eventual Democratic nominee, but it is unclear how that will play out in the primary.

Bloomberg spokeswoman Miryam Lipper, who worked on Hillary Clinton’s 2016 campaign and was the Iowa communications director for Senator Kamala Harris, did not respond directly when asked if the Bloomberg machine will be brought to bear for Biden this week. Lipper said only that there are no updates on the plan to help the Democratic nominee.

Volgy thinks Arizona, where Republicans control all three branches of government, could be turning blue where Washington, D.C., is concerned.

Senator Kirsten Sinema, a moderate Democrat who was elected in 2018 over former Congresswoman Martha McSally, has endorsed Biden, sending out a mailer printed in purple ink to make the announcement.

After McSally lost to Sinema, Arizona Governor Doug Ducey appointed McSally, a retired combat pilot, to replace Senator John McCain, who died in office in 2018. In this year’s race to permanently fill that seat, Democrat Mark Kelly, a former Space Shuttle commander and husband of former U.S. Representative Gabby Giffords, has “vaulted” into the lead in polls and fundraising, Volgy said.

Volgy believes Democrats have a good chance to take Arizona in the presidential race, too.

“I’d say that’s pretty blue,” he said.