WASHINGTON (Reuters) - Bernie Sanders is back for another White House run, but this one promises to be far different than the improbable 2016 presidential campaign that made the Vermont senator a political force.

In the 2020 race, Sanders, who announced his latest bid on Tuesday, will have to fight to stand out in a crowded field of progressives touting issues he brought into the Democratic Party mainstream four years ago. At 77, he also will face questions about his age and relevance in a party increasingly embracing more diverse and fresh voices.

While many of his supporters are sticking with him, some are waiting to see how the Democratic field seeking to challenge Republican President Donald Trump shapes up.

“2020 is not 2016. He had his moment and 2020 may not be his moment,” said Ron Abramson, a New Hampshire immigration lawyer and a Sanders delegate to the 2016 Democratic nominating convention who now is undecided.

Sanders enters the race with clear strengths: broad name recognition, an ability to raise money from small-dollar donors and passionate supporters who flocked to his insurgent 2016 campaign against one of the best-known figures in American politics, Hillary Clinton.

Sanders, an independent democratic socialist who aligns with Democrats in the Senate, pushed Clinton and the party to the left in 2016 and drew fervent support from young and liberal voters with an agenda supporting universal healthcare, raising the hourly minimum wage to $15 and free public college tuition.

Those are mainstream positions for the party now, with Democratic presidential contenders including fellow Senators Elizabeth Warren, Kamala Harris, Kirsten Gillibrand and Cory Booker promoting similar views.

“Some of us get to open doors and others get to walk through them,” said Arnie Arnesen, a liberal radio host and former New Hampshire state legislator who calls herself a Sanders admirer. “Bernie opened the door for progressive politics, but I think he has to recognize there are new voices and a new bench.”

Sanders also will face lingering resentment in some Democratic quarters over the 2016 campaign. His challenge to eventual nominee Clinton split the party and generated tension between its establishment and liberal wings that still exists.

FILE PHOTO: U.S. Senator Bernie Sanders speaks during a news conference on "Raise the Wage Act" legislation on Capitol in Washington, U.S., January 16, 2019. REUTERS/Yuri Gripas/File Photo

DIVERSITY

Sanders already has moved to correct some 2016 missteps.

In January, he apologized to women campaign workers who said they had been harassed or mistreated by male campaign staffers, and he acknowledged the campaign’s “standards and safeguards were inadequate.”

He has been trying to reach out to black and Hispanic leaders after having trouble winning over minority voters in 2016. That could prove challenging again as a white man competing against female, black and Hispanic candidates.

“I really want to be sure the person who I ultimately support is going to take a hard look at diversity and ensure they are reaching out to all communities, particularly people of color and women,” said Lucy Flores, a former Nevada state legislator and U.S. congressional candidate who backed Sanders last time but is uncommitted for 2020.

Ray Buckley, chairman of the Democratic Party in New Hampshire, an influential state with an early nominating contest where Sanders won 60 percent of the vote in 2016, said Sanders’ inner circle of top supporters there is largely with him. But most prominent party activists are shopping the field, Buckley said.

Some Sanders allies expect the crowded field to help him, fracturing the vote enough to give Sanders and his dedicated following more clout.

“It’s going to be real hard for some of the other candidates to stand out, whereas Senator Sanders already has the name recognition and support,” said Tim Smith, a state legislator in New Hampshire and a member of the state’s steering committee for Sanders.

Sanders also will benefit from grassroots groups such as Organizing for Bernie-Draft Bernie and People for Bernie Sanders, which have been building support and organizing for him ahead of his announcement.

His supporters said his decades-long commitment to progressive issues will resonate with voters choosing among candidates with similar views.

“These aren’t platitudes to him,” said Katherine Brezler, co-founder of People for Bernie Sanders. “Having to push somebody to believe these things is not where I need to be. Bernie would not have to be educated about these issues.”

His strengths on the issues, however, may not be enough.

“We need somebody who can tap a broader segment of the electorate,” said Abramson, the 2016 Sanders delegate.