Chafee, a Republican-turned-independent-turned-Democrat former governor and senator of Rhode Island, is looking to position himself as a primary alternative to Clinton, the race's overwhelming frontrunner.
In a phone conversation, Chafee cast himself as a staunch environmentalist who wants to protect civil liberties, avoid foreign entanglements and focus on growing the middle class.
He also looked to demonstrate he is not afraid to attack Clinton, at the same time that other Democrats considering run -- former Maryland Gov. Martin O'Malley, former Virginia Sen. Jim Webb and Vermont independent Sen. Bernie Sanders -- have shied away from direct attacks.
"Considering the premise for invading Iraq was based on falsehoods and considering the ramifications we live with now from that mistake, I would argue that anybody who voted for the Iraq War should not be president and certainly should not be leading the Democratic Party," Chafee said in a phone interview with CNN.
"Yes," Chafee said when asked if he plans on making the Iraq War central to his campaign against Clinton. "That's one of our big differences."
Clinton voted to authorize the Iraq War in 2002, a vote that haunted and helped sink her 2008 presidential campaign against President Barack Obama. At the time a Republican senator, Chafee was the only member of his party to vote against the Iraq War in 2002.
Chafee is an exceedingly unlikely Democratic candidate for president. Even opinion polls that include dozens of names of possible Democratic challengers have not mentioned Chafee as an option.
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Chafee said he thinks Clinton, despite her soaring poll numbers, is beatable and that he will start exploring a run by going to Iowa and New Hampshire to talk with Democratic operatives and voters.
"I don't have a time frame" on when to announce, said Chafee. "I look forward to getting to city and town Democratic committees, calling their chairs, asking when their next meeting is and when I could attend."
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There's one reason this Democrat thinks Hillary Clinton is unqualified