Former Rhode Island Gov. Lincoln Chafee, once a Republican, then an independent, then a Democrat, plans to announce his candidacy for the Democratic presidential nomination next week.

Chafee will do so Wednesday during a speech at George Mason University in Arlington, Virginia, spokeswoman Debbie Rich said.

Chafee surprised many when he formed an exploratory committee in April. He has never won elected office as a Democrat and had only discussed his plans with a few family members and supporters. But after that, he said he was likely to announce his candidacy in June.

He's a distinct longshot. By his own admission, he's not been actively raising money or building the organization needed for a credible bid for the nomination, although he's traveled to the early-voting states of New Hampshire and South Carolina.

Chafee has criticized Democratic front-runner Hillary Rodham Clinton for her Senate vote to authorize the 2003 Iraq invasion and says the next president shouldn't be someone who supported the war. Then a Republican, Chafee was the lone GOP senator to vote against the invasion.

Vermont Sen. Bernie Sanders is challenging Clinton for the 2016 nomination and former Maryland Gov. Martin O'Malley is expected to join the contest Saturday.

Chafee, 62, was appointed to the Senate as a Republican when his father, Sen. John Chafee, died in office, and he won election to the seat the following year. While in Washington, he became known for bucking his party. In addition to opposing the Iraq invasion, he refused to vote to re-elect President George W. Bush in 2004, writing in George H.W. Bush instead.

Chafee lost the seat in 2006 to a Democrat. He left the Republican Party and became an independent in 2007.

In 2010, he was elected to the governor's office. He became a Democrat in 2013 but a few months later decided not to run for a second term. He had poor approval ratings and the 2014 race was expected to be fierce.

Chafee's plans to announce his run Wednesday were first reported by Politico.