PHOTO: The Centers for Disease Control's Tom Harkin Global Communications Center is pictured in Atlanta in this undated image.
Hillary Rodham Clinton and Bill Clinton and Senator Tom Harkin work the grill during Harkin's annual fundraising Steak Fry on Sept. 14, 2014, in Indianola, Iowa.
VIDEO: Sen. Tom Harkin on his 36th annual steak fry and the changing landscape of the Senate.
PHOTO: Chairman Tom Harkin, D-Iowa, arrives for the Senate Health, Education, Labor and Pensions Committee hearing on "Assessing the State of America's Mental Health System" in the Dirksen Senate Office Building on Thursday, Jan. 24, 2013.
PHOTO: Senator Tom Harkin, a Democrat from Iowa, listens during a news conference in Washington, on Tuesday, Dec. 11, 2012.
PHOTO: From left, Sen. Charles Schumer, D-N.Y., Sen. Barbara Mikulski, D-Md., Sen. Tom Harkin, D-Iowa, and Sen. Barbara Boxer, D-Calif.
PHOTO U.S. President Barack Obama participates in a meeting on the Elementary and Secondary Education Act with U.S. Sen. Tom Harkin in the Roosevelt Room of the White House March 10, 2011 in Washington,
PHOTO: Sen. Tom Harkin, talks to reporters after the Senate Democratic policy luncheon, at which Vice President spoke to convince unhappy Democrats file photo.
Video of Tom Harkin during a congressional hearing on peanut butter recall.