It began with heavy flirting in 2012, when Donald Trump, celebrity businessman, declared that President Barack Obama probably wasn't born in America, a suspicion close to the hearts of disaffected white voters, and a notion most Washington Republicans only casually disavowed.

The relationship blossomed last year when Trump, announcing his presidential run, declared that most Mexican immigrants likely are rapists and criminals, then later upped the ante by calling for a ban on Muslims entering the United States. Despite some hand-wringing among Republican elites – or because of it – angry, blue-collar whites warmed to Trump's embrace, packed his rallies and pledged to vote GOP in November.

However, when he hired Steve Bannon, the Breitbart Media CEO and right-wing darling, to run his flagging campaign, Trump officially tied the knot with the so-called "alt-right" – a loose coalition of conservative extremists who love segregation, hate political correctness and yearn for an America that probably never existed. And mainstream Republicans, who had kept mum for years, didn't bother to object.

Yet analysts say the strange-bedfellows union of a bombastic, mercurial tycoon and a once-exiled, aggrieved political movement will almost certainly open a Pandora's Box of dangerous, unstable and potentially violent political forces, ones which mainstream conservatives abandoned, but did not discard, in the wake of the civil rights movement in the 1960s.

The alt-right "is just a rebranding of what people used to call white nationalists," says Heidi Beirich, director of the Southern Poverty Law Center's Intelligence Project, which tracks domestic hate groups and terrorists. "They've rebranded themselves to make themselves not look so bad. But these are the same people that have been pushing this stuff for awhile."

"What's new is, you have a candidate for president, and the new head of his campaign creating a media empire that's explicitly catering to the alt-right," Beirich says. "That's what's different."

However, Trump's decision to stake his campaign on the alt-right constituency will upend the modern conservative movement, tossing over Republicans' mainstream leaders in the process, experts say. At minimum, they say, the volatile pairing of Trump, the GOP, Bannon and the angry, far-right fringe will have repercussions past Election Day and into the next presidential administration.

"Once you've created these monsters, there isn't a whole lot you can do for a long period of time to move them back to a less significant force of society," says Norm Ornstein, a political scientist and senior fellow at the American Enterprise Institute, a right-leaning think tank. After the election, he adds, "we better be prepared for some turmoil."

A term largely credited to Richard Spencer, director of the National Policy Institute, a white nationalist think tank, the alt-right describes an ideology based on the preservation of "Western civilization" as defined by race. It also blends in libertarian free-market ideas, "traditional" views against women's and gay rights and considers other races biologically inferior.

"We reject the notion that race is some sort of sociological optical illusion" and that all men are created equal, said Jared Taylor, founder of American Renaissance, a leading alt-right website. Interviewed on NPR's The Diane Rehm show Monday, Taylor said race "is a biological fact, whether we wish to recognize it or not."

Nicole Hemmer, a scholar at the University of Virginia's Miller Center for Public Affairs says the alt-right is essentially an updated version of the Jim Crow-era White Citizens' Councils – the so-called "uptown Klan" – that popped up in the South. Like the alt-right, she says, the goal then was to whip up middle-class resistance to civil rights and court-ordered desegregation.

"After passage of the Civil Rights Act, [the WCCs] began to moderate their language" to make their positions on race more palatable for conservative Republicans and educated whites, Hemmer, who is also a contributing editor at U.S. News, says. Calls for "state's rights" replaced the more toxic demands for "segregation" in the WCC lexicon, and the alt-right's jeremiad against "political correctness" serves the same purpose.

The movement's leaders, however, say their alignment with Trump and the GOP is a pragmatic attempt to remain atop the racial hierarchy in the face of rapid demographic change. After years in exile on the political fringe, Trump's embrace of their views – coupled with the scorn they drew from Hillary Clinton in her speech attacking white nationalism last week – is a turning point.

"It's hugely significant," Spencer told Slate.com in an interview last week. "When a presidential candidate – and indeed the presidential candidate who is leading in most polls – talks about your movement directly, I think you can safely say that you've made it."

That's the problem, says the SPLC's Beirich: The alt right's ideas, once seen as distasteful and outdated, are now part of the American political dialogue. Because of Trump, and inaction by Republican leaders, she says, a major-party presidential nominee has legitimized a small but highly vocal constituency.

"It was always basically understood at the national level that these are the worst ideas that America has come up with," she says. And it shows no sign of fading.

According to the SPLC, 2015 saw a spike in violence perpetrated by white extremist groups, including a bombing at an NAACP office in Colorado Springs, Colorado, a series of arson attacks on black churches in several Southern cities and the shooting of nine black churchgoers in Charleston, South Carolina.

"The armed violence was accompanied by rabid and often racist denunciations of Muslims, LGBT activists and others – incendiary rhetoric" fomented by "a number of mainstream political figures" and amplified "in the right-wing media," according to an SPLC report.

"Reacting to demographic changes in the U.S., immigration, the legalization of same-sex marriage, the rise of the Black Lives Matter movement, and Islamist atrocities," the report states, "these people fostered a sense of polarization and anger in this country that may be unmatched since the political upheavals of 1968."

At the same time Trump began to woo the alt-right last year, "hate groups continued to flourish," according to the report. According to its survey, the number of right-wing hate groups, shot from 784 in 2014 to 892 in 2015.

Unlike previous GOP presidential candidates who spoke in code words and "dog whistles" about race and class, Beirich says, Trump said what the alt-right had been waiting to hear: Illegal immigrants are stealing jobs, African Americans are living in squalor and crime and Muslims must prove they're not terrorists before they can come to America.

"Everything is being validated and they're saying, 'We're not some fringe thinkers – we're in the mainstream," Beirich says.

Get used to it, says Ornstein, co-author of the book, "It's Even Worse Than It Looks: How the American Constitutional System Collided With the Politics of Extremism."

"Part of what's' struck me in the past, is, with some notable exceptions – the Ku Klux Klan in the South is a notable exception – you had no notable organization of people. They tended to be more isolated and more atomized."

But in the era of Twitter and the internet, the alt-right has found it far easier to organize and get their message out, Ornstein says. Trump, he says, emerged "with the most blatant appeals to the base instincts of people and winning a [presidential] nomination. Which means he's granted a level of instant legitimacy that hadn't existed before."

Beirich, however, says actual violence may be the result -- especially since "we don't know what these people would do once they're in power" should Trump pull off an upset win. But Trump, she says, has already salted the ground by insisting that, even though he's trailing Clinton by double-digits in some swing states, if he loses it's because the election is rigged.

If that happens, "now we've got a highly charged bunch of angry people who feel like their last stand was lost," she says. "What are they going to do then? More violence? More domestic terror? I think that's a good bet. That whole movement runs off of rage."

Taylor, the American Renaissance publisher, wouldn't speculate about a Trump loss. But he also declares that the movement he helped create is far larger than one candidate.

"People like to call it 'the American experiment.' I don't like to think of my country as an experiment – a bunch of chemicals sitting over a bunsen burner," he told Rehm.

Trump "has stumbled onto a number of policy proposals that are congruent with those that would be supported by the alt-right. His instinct is the country is changing in disagreeable ways. These are policies that appeal in powerful ways to many ordinary Americans that see their country slipping through their fingers."