Nina Turner

Former Ohio State Sen. Nina Turner speaks at the Democratic National Committee's 22nd Annual Women's Leadership Forum National Issues Conference in Washington, Friday, Oct. 23, 2015.

(Jacquelyn Martin, The Associated Press)

CLEVELAND, Ohio -- Nina Turner will remain a Democrat.

The former Ohio state senator from Cleveland said Monday evening that she has rejected an offer to run for vice president this fall on the Green Party's ticket.

Turner had been among the most prominent supporters of Bernie Sanders' unsuccessful bid for the Democratic presidential nomination. Jill Stein, the Green Party's presumptive nominee for president, asked Turner over the weekend about joining her campaign, which is aiming to attract Sanders' supporters.

"I'm going to keep fighting in the party, even though I'm disappointed," Turner said in a telephone interview. "I'm a Democrat, and that's worth fighting for."

Turner upset Democrats at their national convention last week by publicly showing that disappointment, even after Sanders fell in line graciously behind one-time rival Hillary Clinton. She said she had been scheduled to deliver one of the speeches placing Sanders' name in nomination but was dumped at the last minute.

A former Cleveland city councilwoman, Turner is often mentioned as a future candidate for mayor. She left a top post at the Ohio Democratic Party last fall after switching her support from Clinton to join Sanders in a high-profile role. The move raised eyebrows at the time, as Clinton's husband, former President Bill Clinton, helped Turner raise money for her failed Ohio secretary of state bid in 2014.

"What I really care about is making this progressive agenda more actionable," Turner, who had a hand in crafting the new Democratic platform, said Monday.

She added that she is not prepared to endorse Clinton.

"The media keeps asking me about an endorsement, but she hasn't asked me for an endorsement," Turner said. Her team hasn't asked me for an endorsement."

Stein's offer to Turner was first reported Sunday night by cleveland.com. Turner said then that she would have a decision before the Green Party opened its convention later this week in Houston. She said Monday that she wanted to have an answer for Stein sooner, rather than later, as the Massachusetts physician had other options.

Later Monday, Stein announced human rights activist Ajamu Baraka as her running mate.