Then, he was challenged from the right in the Republican primary by Cranston Mayor Steve Laffey. He lost in November to Democrat Sheldon Whitehouse.
Chafee felt rejected by the GOP, which no longer seemed willing to include moderate Republicans like himself.
The worst moment, he says, was when conservative commentator Ann Coulter wrote a critical column titled, "They Shot the Wrong Lincoln."
"I was waiting for someone to speak out" against her, Chafee says of the party's leaders. "But no one did."
After losing the race, he taught at Brown, his alma mater, and wrote a book titled Against the Tide. In 2008, Chafee voted for Barack Obama, his first vote for a Democrat. He weighed joining the Green or Libertarian parties but found neither a good fit. Chafee considered Rhode Island's fledging Moderate Party but thought the name sounded "wishy-washy."
Running as an independent frees him from defending party positions that are not his own, Chafee said — a liberation.
A Rasmussen survey in May, the most recent public poll available, gave him a narrow lead over Caprio and likely Republican nominee John Robitaille.
"I think this trend will continue, and it should be a wake-up call to the parties," said Angus King, who was elected and re-elected governor of Maine as an independent in the 1990s. "If they continue to spend more time on picking each other apart and less time on problem-solving, the American people are going to find other options."
Still, running as an independent isn't easy, one reason that Democrats and Republicans have dominated American politics since the Civil War.
Not since Theodore Roosevelt's Progressive bid in 1912 has anyone besides a Democrat or Republican finished as high as second in a presidential campaign. In 1992, third-party contender Ross Perot helped shape the presidential race but ended a distant third with 19 percent of the vote.
Two current members of the Senate, Joe Lieberman of Connecticut and Bernie Sanders of Vermont, were elected as independents. Both caucus with the Democrats.
Independents for any office lack the ready-made political infrastructure that major-party candidates can rely on, making fundraising problematic and voter outreach more difficult.
"You don't have party lists, and what that means is that you have to build an organization from scratch," Cutler says. Maine provides public financing for gubernatorial elections, but the thresholds set make it hard for independents to qualify.
That means independents have their best shot in small states such as Rhode Island and Maine with relatively low campaign costs. With a New England tradition of independence, both states have more unaffiliated voters than either Democrats or Republicans.
It also helps when candidates such as Chafee have the family wealth to loan themselves significant amounts of money. Chafee and Cutler each estimate that credible gubernatorial campaigns in Rhode Island and Maine, respectively, can be run for about $2 million. In Massachusetts, Cahill puts the price tag at $4 million-$6 million.
Independents also have to battle for credibility.
"The biggest obstacle an independent faces is convincing the voters that they're not a wasted vote, that they have a realistic chance," King said. Independent candidates who look strong in the summer often fade in the fall, as voters focus on the elections.
Then there are the attacks that independents have to fend off from both sides.