Retiring Sen. Tom HarkinThomas (Tom) Richard HarkinSenate GOP rejects Trump’s call to go big on gun legislation Trump should require federal contractors to follow the law Orrin Hatch, ‘a tough old bird,’ got a lot done in the Senate MORE (D-Iowa) says Hillary ClintonHillary Diane Rodham ClintonKoch-backed group launches six-figure ad buy against Heitkamp Trump keeps up 'low IQ' attack on Maxine Waters GOP leaders to Trump: Leave Mueller alone MORE should start visiting Iowa more if she plans on launching a 2016 presidential bid.

"If she's going to run, she should start getting out here," Harkin told the Quad-City Times on Friday.

He touted Clinton as a strong candidate that "would bring a lot of experience and knowledge that we haven't had in that White House for a long long time. "I mean just from the git go ... I think she's proven herself over all these years," Harkin added.

The 30-year Senate Democratic veteran, who himself ran for president, also encouraged Maryland Gov. Martin O'Malley and Vice President Joe BidenJoseph (Joe) Robinette BidenKentucky candidate takes heat for tweeting he'd like to use congressman for target practice The Hill's 12:30 Report Biden hosting fundraiser in Miami MORE to stump in his state.

The race to replace Harkin in the Senate is heating up. Rep. Bruce Braley is the only Democrat in the race so far. Republicans include State Sen. Joni Ernst, businessman Mark Jacobs and former attorney general Matt Whitaker.