Sen. Bernie Sanders is running for president in 2020 perhaps for one reason more than any other: to complete the work he began.

The independent from Vermont came far closer to winning the 2016 Democratic primary than many would have guessed and has since watched many of his ideas become more mainstream within the Democratic Party. To his supporters, taking another shot at the Oval Office makes sense. But with the 2020 Democratic field already shaping up to be quite different from the one Sanders competed in four years ago, claiming victory could be even more difficult.

Concerns about Sanders’s ability to connect with voters of color plagued his 2016 campaign, and recent comments from some former staffers have recalled those difficulties. Despite Sanders’s past popularity, the question is: Can Sanders win the Democratic nomination in the Trump era against the most diverse candidate field in history?

Obviously, Sanders think he can. The presidential candidate told SiriusXM’s “Make It Plain with Mark Thompson” Tuesday:

“I think we have a message that is going to resonate, resonate all over this country, and in the African-American communities. It’s going to be a message which says we’ve got to end institutional racism, we’ve got to pay special attention to those people who have been hard hit economically. We have to invest in urban communities, and we have to deal with all of the massive disparities that currently exist in American society.”

According to The Washington Post, the Sanders campaign will advocate for a Medicare-for-all health-care system, a Green New Deal in response to growing concerns about climate change and a $15-an-hour minimum wage for all Americans.

Sanders will also tout proposals to mandate breaking up the biggest Wall Street banks; free tuition at public colleges; lower drug prices with aggressive government intervention; new labor law to encourage union formation; curbed corporate spending on elections; paid family and medical leave; gender pay equity; and expanded Social Security benefits for the elderly and disabled, aides said.

Sanders’ criminal justice platform will include legalizing marijuana, ending cash bail throughout the U.S., and abolishing private prisons, while he will also run on the standard Democratic policy goals of protecting young immigrants brought to the U.S. as children and limiting the sale and distribution of guns.

All of those issues are of interest to voters of color, but Sanders struggled to convince the majority of them in 2016 that he had better policy solutions to these concerns than did Democratic rival Hillary Clinton. In the South Carolina primary, Sanders won 14 percent of the African American vote, according to exit polls. Clinton, the eventual Democratic nominee, took 86 percent of the vote.

Winning the majority vote of African Americans — and Latinos, Asian Americans and other voters of color — could be even more challenging as more voters seem excited to get behind candidates they feel better represent them in terms of race, gender and sexual orientation. Sanders appears to be calling on Americans to look beyond identity in determining their choice for the next president.

“We have got to look at candidates, you know, not by the color of their skin, not by their sexual orientation or their gender and not by their age,” Sanders told Vermont Public Radio on Tuesday. “I mean, I think we have got to try to move us toward a nondiscriminatory society which looks at people based on their abilities, based on what they stand for.”

Surely many liberal voters agree with Sanders. Yet they question whether he is the most capable candidate to respond to the country’s ongoing issues related to race, gender and faith that have dominated headlines under the administration of a man many Americans consider to be one of the most divisive presidents in recent history.

In a New York Times article published Sunday, nearly two dozen of Sanders’s current and former advisers and staff members spoke about the 2016 campaign’s inability to connect consistently with African American voters. The lawmaker’s initial leadership team was all white and focused heavily on states with white majorities, such as Iowa and New Hampshire, giving the impression to voters of color that Sanders’s message did not include them.

John Solomon told the Times he was originally hired as an organizer for the Sanders campaign before aides assigned him to driving people in a truck around Iowa. “It’s almost like they didn’t need us for anything,” Solomon said. “It was kind of like, you have black staff just to say you have black staff.”

The 2020 race also comes with at least five women competing for the Oval Office after the #MeToo movement rocked not only Hollywood but politics. The Sanders team recently had its own reckoning, parting ways with top advisers after reports of discrimination, sexism and harassment by co-workers against women on his campaign staff. Sanders apologized to female staff members, saying he was unaware of the incidents.

Ultimately, most Democrats being surveyed are looking for someone who can beat President Trump. And, based on polling, Sanders enters the race as a front-runner with many on the left. But when it comes to women and people of color, who make up some of the most influential voting blocs on the left, the veteran lawmaker still has to prove himself — perhaps now more than before and against stiffer competition.