Former U.S. senator and Rhode Island governor Lincoln Chafee will seek the nomination of the Democratic party to run for U.S. President in 2016.

"We must deliberately and carefully extricate ourselves from expensive wars," Chafee said on Wednesday, June 3.

Chafee has served as a Republican and an Independent but has never before run for office as a Democrat. Analysts say he will aggressively attack presumptive front-runner Hillary Clinton on her foreign policy record.

In his announcement speech, he called for the U.S. to move to the metric system and end capital punishment. He also advocated an "open-minded approach" to drug trafficking.

But his priority would be to end all U.S. wars. "Let's wage peace in this new American century," he said.

Chafee joins Clinton, Vermont Senator Bernie Sanders and former Maryland Governor Martin O'Malley in the Democratic primary race.

Chafee has so far been the Democrat most willing to directly criticize Clinton, particularly over her Senate vote in favor of the Iraq War.

"I don't think anybody should be president of the United States that made that mistake," Chafee told the Washington Post in April.

Chafee's rivals have already built robust campaign operations with staff across the country, a step he has yet to take, the BBC notes.

Before splitting with the Republicans he had consistently been called the party's most liberal lawmaker.

In 2002 he was the only Republican member of the Senate to vote against authorizing the invasion of Iraq.