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Indeed, “discomfort with open division is part of the DNA of the nation,” says historian Rick Perlstein, author of The Invisible Bridge: The Fall of Nixon and the Rise of Reagan. “It’s all about repressing this original fissure: Slavery. The entire history, for the first half of the 19th century, is this all-consuming attempt to keep this genie in the bottle.”

To get slave-owners to at least pay lip service to “life, liberty and the pursuit of happiness,” the Founders compromised that three out of every five slaves would be counted in a state’s population when apportioning congressional seats. Slave states wielded this inflated electoral power to ensure slavery continued in the new republic, while the Compromise of 1850 facilitated slavery’s westward spread and made the federal government responsible for recovering “fugitive” slaves.

These compromises “came at a tremendous cost,” says historian Manisha Sinha, author of The Slave’s Cause: A History of Abolition. “If you think of slavery as a gross abuse of human rights, then compromise doesn’t sound so good.”

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All of this was possible, says historian Thomas Frank, in part because “there was a time when the parties were not divided by ideology or by their place on the political spectrum. The parties were regional and ethnic.”

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“The election of Ronald Reagan was a symbol of the eclipse of the Rockefeller Republicans by the Barry Goldwater wing, sending a signal to the party to get on board,” says Corey Robin, professor of political science at Brooklyn College and the City University of New York Graduate Center.

Reagan used his bully pulpit to popularize the idea of getting “the government off the backs of the people.”

“The conservative wing of the GOP established hegemony over not just the Republican Party, but the American political order,” says Robin.

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“[Republican Party patrons have] turned the GOP into a kind of Leninist party of the Right, one in which no dissent is allowed after the course has been set,” says historian Nancy MacLean, author of Democracy in Chains: The Deep History of the Radical Right’s Stealth Plan for America. “It wants to dramatically diminish the power of the federal government in order to remove the reins from capitalists.” And yet, she says, “We are still operating as a nation as if there is a Republican Party.”

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For inspiration, today’s progressives might look back to the anti-slavery movement, which went from a relatively small band of uncompromising, “radical” activists to controlling the presidency and Congress. 

“Abolitionists were never anywhere near a majority in the North or anywhere else,” says Eric Foner, professor emeritus of history at Columbia University. “They were a vanguard.”