Retiring Sen. Tom HarkinTom HarkinGrassley challenger no stranger to defying odds Clinton ally stands between Sanders and chairmanship dream Do candidates care about our health or just how much it costs? MORE (D-Iowa) says Hillary ClintonHillary Rodham ClintonSecret Service agent wrote she wouldn't take a bullet for Trump GOP rep: 'Plausible' that 3 million fraudulent votes were cast Dems unveil infrastructure plan, reach out to Trump 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.

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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 BidenJoe BidenThe Women's March was about tantrums, not women Biden boards train home to Delaware after Trump's inauguration Overnight Tech: Meet the key players for Trump on tech | Patent chief staying on | Kerry aide goes to Snapchat | Uber's M settlement 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.