DES MOINES, Iowa (AP) — When Iowa Sen. Tom Harkin completes his last year in office, the longstanding lawmaker may take a certain brand of liberal Midwestern populism with him.

A so-called "prairie populist," Harkin was raised amid the social programs of the depression, witnessed the horrors of the war in Vietnam and charged into politics vowing to fight for the working classes, minorities and those with disabilities. Many of his like-minded Midwestern peers are no longer in government.

But until he walks out the door in January 2015, the 74-year-old Harkin shows no signs of slowing down his fight for the progressive causes he has championed throughout his nearly 40-year career. In recent months he has been advocating for President Obama's health care overhaul, pushing for higher federal minimum wages and promoting anti-discrimination legislation.

While deciding to retire, "I wanted to get some things done," said Harkin, adding that he hopes others will carry on his fight. "I sure hope that there are going to be more prairie populists coming along. I see populism as a positive force, not a negative force."

An Iowa native, Harkin was first elected to the Senate in 1984, after 10 years in the House of Representatives. He ranks seventh in seniority, and fourth among Democrats. He is chairman of the health, education, labor and pensions committee and a senior member of the agriculture committee.

Harkin considers winning bipartisan support for the 1990 Americans with Disabilities Act his key legislative achievement. Harkin sought the bill because of his brother, who was deaf, and he used sign language to speak about the legislation on the Senate floor.

"I just saw how he was deaf, he was discriminated against," Harkin said. "His choices, his options were limited. He wouldn't accept that. It was always a struggle."

More recently, Harkin served as a key salesman of President Barack Obama's 2010 health care bill to the left. He has remained an advocate as the program has come under fire for a faulty enrollment website and for triggering insurers to cancel some individual policies. Harkin has also been active on a slew of other legislative priorities of late, including introducing legislation that would expand early childhood education.

"I just want to leave a legacy. Government is still an honorable profession, so is politics," said Harkin. "It's not bad, it's good. You can do things that make a positive difference in people's lives."

Pennsylvania Sen. Bob Casey, a Democrat who has worked with Harkin on health and education legislation, said Harkin never forgets that he is working for people in need. He recalled a speech Harkin made about his father — a coal miner with an eighth grade education — getting a Medicare card for the first time and what it meant to him.

"(He's) someone who has a passion for those who need a voice," Casey said.

Harkin is part of a long tradition of Midwestern progressive politics that focuses on civil rights and government aid for the needy, as well as support for farming and environmental causes. This movement produced politicians like Hubert Humphrey, Eugene McCarthy and Walter Mondale, all Minnesota Democrats who unsuccessfully sought the presidency. George McGovern, a South Dakota lawmaker and presidential candidate, is another member of the clan.

But the senators who have more recently represented this branch of the Democratic party have largely left office. They include Tom Daschle of South Dakota, Byron Dorgan of North Dakota and the late Minnesota Sen. Paul Wellstone. Other longtime Democrats departing with Harkin are Montana Sen. Max Baucus and Michigan Sen. Carl Levin.

"I hope he's not the last, but (Harkin's) certainly one of the most prominent we've had in the Midwest," said Daschle, who now works for the DLA Piper law firm.

Harkin launched an unsuccessful presidential bid in 1992, with a campaign that focused on traditional liberal politics. He has not pursued higher office since, but has enjoyed the position of leading Democrat in a state where the first presidential voting is held, hosting candidates at his annual "Steak Fry" fundraiser.

Harkin's exact post office plans are unclear, though he has said he expects to be involved with a namesake institute at Drake University. Friends and colleagues say he will likely remain a public figure.

"I think there's no chance he fades away," said longtime political adviser Jeff Link.

U.S. Rep. Bruce Braley, the Democrat running to succeed Harkin in the Senate, has vowed to continue in his liberal footsteps. "The goal is to continue to fight for policies that are going to give people a shot at the American dream and expand the middle class," Braley said.