It’s official. On Saturday, Iowa’s longest-serving Democratic Senator, Tom Harkin, told the Des Moines Register he will not be seeking re-election for a sixth term in 2014.

One of the Senate’s leading liberal voices, the 74-year-old senator has represented the state of Iowa for almost 40 years at the federal level and has become somewhat of an institution for progressivism.

“To walk away from this position and this power is not an easy thing. But I think it’s the right thing,” Harkin told the Des Moines Register.

Harkin graduated from Iowa State in 1962 with a degree in government and economics and served in the U.S. Navy until 1967.

The future senator then moved to Washington, D.C. where he worked as an aide to Democratic U.S. Congressman Neal Smith and later received his law degree from the Catholic University of America.

Returning to Iowa, Harkin was elected to the U.S. House of Representatives in 1974 and went on to win his seat in the U.S. Senate in 1984, where he has since won five consecutive reelections.

For many, Harkin will be long remembered for his commitment to progressive policies and his support for people with disabilities, which included the Americans with Disabilities Act of 1990, arguably his most famous legislative accomplishment.

Furthermore, his support for the 2010 Affordable Care Act and other Democratic policy initiatives will cement his legacy in the Senate and among his Iowa constituents.

“There’s no doubt he will be remembered for championing for people with disabilities,” said Kyle Upchurch, senior in political science and former intern in Harkin’s office. “Additionally, he was always committed to his constituents. … He and his staff were very passionate about serving Iowans.”

Since Harkin’s announcement on Saturday, the political world has been buzzing with potential replacements for the senator.

This may pose trouble for democrats, who currently hold a 55-45 edge in the Senate over republicans. Two independent senators caucus with democrats, but must defend 21 of the 35 seats up for reelection in 2014.

Harkin’s departure could potentially help republicans take control of the Senate in the 2014 midterm elections.

“For the republicans, this is a golden opportunity to try and regain an open seat with no incumbent. Most Senate races that result in a turnover are races for open seats,” said Steffen Schmidt, professor of political science, in a blog post.

“For Democrats, the mission is no less critical. Retain a seat of one of the most influential, senior members of the party and hang on to the relatively slim majority the party has in the Senate.”

Schmidt said there are many names on the republican side who may consider running for Harkin’s seat.

Staunch conservatives like Rep. Steve King and evangelical voice Bob Vander Plaats are well positioned among Iowa’s traditional, conservative base to launch a campaign.

Additionally, Iowa Gov. Terry Branstad, Rep. Tom Latham, Iowa GOP Chair A.J. Spiker, and former Mitt Romney campaign head David Oman may be interested in running as well.

On the Democratic side, one possible successor to Harkin is Rep. Bruce Braley, though state Sen. Jack Hatch and former first lady Christie Vilsack may be mulling a run, according to Schmidt.

“Congressman Bruce Braley seems to be the frontrunner. There has been a great deal of buzz about him,” Schmidt said. “He is the up-and-coming Democratic political ‘star,’ and he has done well getting reelected. Moreover, he has been very visible in the Des Moines area media market in the past six years.”

Soon after Harkin’s announcement, Braley released a statement saying, “Iowans deserve a senator who will continue Tom Harkin’s legacy of strengthening the middle class and standing up for Iowans who don’t have a voice. While Sen. Harkin’s shoes are impossible to fill, over the coming days my family and I will carefully weigh a possible candidacy for Senate.”

Abhishek Vemuri, senior in electrical engineering and president of the ISU College Democrats, said he hopes his club will strongly support any Democrat who wins the nomination to run for Harkin’s seat, as well as each congressional district.

“I’m hoping the College Dems will launch a huge push to support whoever the democratic candidate is,” Vemuri said. “But we also wish Sen. Harkin the best in whatever route in his life he takes next.”

There is also the question of what Harkin will do once he retires.

Schmidt said the senator will be welcome to come to Iowa State to work at the new Harkin Institute of Public Policy, which will house all of Harkin’s papers.

“As to what Sen. Harkin will do, one rumor has it that he will want to be resident scholar for his papers at the Harkin Institute at Iowa State,” Schmidt said. “If nothing else, he clearly will write a book on his signature legislative legacy, the Americans with Disabilities Act, probably his greatest accomplishment, which changed life for Americans forever and has left its mark in every town and building in the United States and in every hiring and education policy.”

Schmidt also left the possibility open for Harkin to work in some capacity in the Obama administration, though nothing is for sure yet.

Until his retirement, Harkin said he will work hard to continue to fight for Iowans as he finishes the last two years of his career in Washington.