After winning the primary, Kaptur will face the winner of the Republican primary, Samuel "Joe" Wurzelbacher, who became known as "Joe the Plumber" when he voiced worries about Obama tax policies during the 2008 presidential campaign.
If this marks the end of Kucinich's career as an elected politician, he will have left memories that are viewed variously by many Americans as good, bad, or just quirky.
"They're out of control," he said of President Bush and Vice President, Dick Cheney, during a late 2007 presidential debate. A relenteless critic of the Iraq war and the way it was launched, Kucinich outlined a provocative response before the CNN audience. "It's called impeachment, and you don't wait. You do it now."
He added: "I'm actualy the only one on this stage who voted against the war, voted against funding the war one hundred percent of the time."
In the same debate, CNN correspondent Wolf Blitzer raised the issue of new homeland-security policies under the Bush administration's war on terror. "You voted against the Patriot Act," Mr. Blitzer said to Kucinich.
"That's because I read it," he fired back, to loud applause from the audience.