Vermont Sen. Bernie Sanders wants to lead a "political revolution" -- he said it hundreds of times during his insurgent campaign for the Democratic presidential nomination.

That was never going to happen in the Democratic Party. The party of Franklin Roosevelt, Lyndon Johnson and Bill Clinton is built for evolution, not revolution. Former Secretary of State Hillary Clinton, Bill's wife, fought off Sanders' stiff challenge and will be formally nominated later this month.

But the dream of progressive revolution lives on, and not because Clinton has embraced much of Sanders' core agenda, moving left on health-care reform, college affordability and other issues. Dr. Jill Stein, the leader of the minor Green Party, says she's willing to step aside and let Sanders take the party's top spot for the presidential election.

"I've invited Bernie to sit down and explore collaboration," she told The Guardian. "Everything is on the table. If he saw that you can't have a revolutionary campaign in a counter-revolutionary party, he'd be welcomed to the Green Party. He could lead the ticket and build a political movement."

The Green Party, which is expected to select Stein at its presidential nominating convention in August, advocates aggressive environmental policies, social justice, grassroots democracy and other progressive priorities. Like the Libertarian Party on the right, Green Party leaders see an opportunity to break into the big time in this election. Both Clinton and presumptive Republican presidential nominee Donald Trump have historically high "unfavorable" ratings for major-party candidates.

A Reuters/Ipsos poll conducted last week found that 21 percent of likely voters "will not back Trump or Clinton." Reuters reports, "Demand for an alternative could be decisive in hotly contested battleground states."

A key problem for the Green and Libertarian parties is that most Americans still haven't heard of their presidential candidates. Only 16 percent of likely voters in the Reuters/Ipsos poll were "somewhat familiar" with Stein, for example. But Sanders as the Greens' presidential candidate -- presumably with Stein as his vice-presidential running mate -- would dramatically raise the party's profile and likely upend the fall campaign.

There hasn't been a major-party realignment in the United States since the 19th century, when the Republican Party rose up out of the ashes of the Whig and Know-Nothing (American) parties. So it could be overdue. But while most political observers believe it's the Republican Party that's in trouble, thanks to Trump bringing nativists and racists into the party and driving out traditional economic conservatives, Stein is convinced the Democratic Party is just as ripe for history's dustbin.

"It's a mistake to think the lesser of two evils will fix things," she says of the possibility that Sanders' supporters will vote for Clinton in November. "A lot of people are in the target hairs of a neoliberalist nightmare. Wars are bankrupting us morally and financially."

Stein insisted that Sanders, a long-time independent who joined the Democratic Party solely to run for president, could achieve his "political revolution" by joining the Greens.

"If he continues to declare his full faith in the Democratic Party, it will leave many of his supporters very disappointed," she said. "That political movement is going to go on. It isn't going to bury itself in the graveyard alongside Hillary Clinton."

Sanders has not responded to Stein's offer. He has expressed enthusiasm for how the Democratic Party platform has taken shape and is expected to endorse Clinton this week.

-- Douglas Perry