Bernie Sanders. Scott Eisen/Getty Images OMAHA, Nebraska (AP) — Bernie Sanders, who attracted millions of college-aged and young adults to his presidential campaign last year, is following through on a promise he made when he left the race: to promote younger leaders for the Democratic Party.

It may not seem the most likely role for the slightly stooped, white-haired, 75-year-old Vermont senator. But Sanders was rallying support on Thursday for Omaha's Democratic mayoral candidate Heath Mello, who's half his age.

While the Democratic Party searches for a path back to power around the country, Sanders is using his popularity to draw thousands at events to promote next-generation Democrats, though his effectiveness so far is unclear. He's on an eight-state circuit of rallies with Democratic National Committee leaders, visiting states Trump carried in the November election.

"We need to transform the Democratic Party," Sanders said in Louisville's packed Palace Theater while headlining a Democratic Party rally in Kentucky Tuesday. "We need to open the doors of the Democratic Party to working people and to young people."

Most of the 17 candidates Sanders' political action committee has endorsed this year, including Mello, are in their 30s and 40s and generally reflect Sanders' call for newer faces in a variety of political positions.

Some are direct products of the Sanders campaign, such as Khalid Kamau, who was elected to the South Fulton, Georgia, City Council on Tuesday. The 40-year-old Atlanta-area activist in the Black Lives Matter movement volunteered for Sanders' campaign last year.

Others reflect Sanders' challenge to the party establishment, such as Tom Pierrello of Virginia. The 43-year-old former U.S. House member and adviser to President Barack Obama is seeking the Democratic nomination for governor against Virginia Lieutenant Governor Ralph Northam.

But Sanders is using his popularity with younger Democrats to chiefly to inspire, rather than directly recruit, the younger faces he says the party needs.

It's a tricky dance for Sanders, an independent who does call himself a Democrat — rather, a democratic socialist — but sought the 2016 Democratic presidential nomination and aligns with the party's minority in the Senate.

Still, Sanders' call for tax-supported free college tuition and, more broadly, his indictment of the political influence of the wealthy drew millions of younger voters to his cause during last year's campaign.

In the primaries and caucuses he captured 70 percent of the 30-and-younger vote, and those 2 million votes far exceeded the combined totals for Democrat Hillary Clinton and Republican Donald Trump. Among Democratic primary voters alone, Sanders won a solid majority of support from voters ages 45 and younger.

"Just seeing him inspires people," said Shannon Jackson, executive director of Sanders' PAC. "Where he draws such numbers of people, they are inspired by his message."

On Tuesday, Sanders brought many of the roughly 2,800 in Louisville to their feet by reprising key lines from his 2016 campaign, including: "Our job is to take on the moneyed interests. And the only way I know as to how we do that is by bringing millions of people into the political process, with a newborn understanding that we have got to get involved."

After that campaign, he didn't rule out a second bid for the White House. In four years, Sanders would be 79 — nine years older than Trump, who is the oldest ever to assume the White House.

It takes more than being a younger Democrat for a candidate to gain Sanders' support. His political action committee decided against endorsing 30-year-old Georgia Democrat Jonathan Ossoff, a former congressional staffer who qualified Tuesday for a June 20 runoff House election after raising more than $8 million in mostly out-of-state contributions.

Sanders did endorse and campaign for 46-year-old Democrat James Thompson, a civil rights lawyer, ahead of his closer-than-expected, losing effort in a special U.S. House election in Kansas last week. Thompson raised a fraction of Ossoff's haul, and in smaller contributions, a hallmark of Sanders' own campaign.

He's also backed Kimberly Ellis, a 43-year-old California activist who has led a Democratic women's advocacy group and is campaigning for California Democratic Party chairwoman. She supported Sanders in last year's primary.

Some Democrats say Sanders is headed in the right direction, but must do more.

Rep. Tim Ryan, a Democrat from eastern Ohio, said the party needs to be more aggressive in organizing target voters, whom he described as working and middle class voters who turned to Trump, and recruiting from within them.

"We need newer faces across the board: Veterans, police officers, teachers, coaches, firefighters that can improve our party's brand at least visually," said Ryan, who unsuccessfully challenged Nancy Pelosi for Democratic House minority leader late last year.

Such candidates, no matter their age, Ryan said, "can be powerful, as long as they are driving an economic message."