It used to be that when you said you were a Democrat, no one knew if you were a liberal or a conservative. When you said you were a Republican, no one knew if you were a conservative or a liberal. Now there are no liberal Republicans and no conservative Democrats. And so governing has become a partisan pendulum at best or gridlock at worst, and real progress feels impossible because the parties have lost the thing that allowed them to govern: common ground. The beginning of the end of that common ground was 1968. The presidential campaign of that year planted seeds in both parties that still bear fruit today.

When the 1968 presidential campaign began, a liberal Republican was a frontrunner for the nomination, and a Southern Democrat with a conservative history had a lock on the Democratic nomination. The liberal Republican candidates, George Romney and Nelson Rockefeller, and the conservative Republican candidate, Ronald Reagan, lost the nomination to the comparatively centrist Republican Richard Nixon. The Democratic front runner, incumbent president Lyndon Johnson, dropped out of the race after a shockingly strong challenge from the left side of his own party, first from Senator Eugene McCarthy and then by Senator Robert Kennedy.

Bernie Sanders was 27 years old when he moved to Vermont in 1968 and watched with as much surprise as President Johnson and the rest of the country when Gene McCarthy “won” the New Hampshire primary by finishing a strong second to LBJ. The model for the Bernie Sanders insurgency from the left against the Democratic Party establishment’s front runner was created by McCarthy in 1968. After the assassination of Bobby Kennedy on the night he won the California primary followed by a chaotic Chicago convention with rioting in the streets, the party establishment delivered the nomination to LBJ’s heir apparent, Vice President Hubert Humphrey, who then went on to lose in November, as has every Democratic establishment nominee since then who has had to overcome a serious primary challenge from the left. Establishment Democrats are always the last to know when something new and important is happening in their party. So too with establishment Republicans. None of them saw Trumpism coming.

Candidates like Sarah Palin in 2008 and Herman Cain in 2012 helped Republican voters develop a tolerance for Donald Trump’s fact-free campaign pronouncements. But the essence of Trump’s appeal to what has come to be known as the Trump base was born in 1968.

Two years before he ran for president as a third-party candidate in 1968, Alabama governor George Wallace said, “Hell, we got too much dignity in government now. What we need is some meanness.” Wallace was the first presidential candidate to use the protesters in his audiences to show off his meanness. Trump was the second. “I’d like to punch him in the face,” Trump told a campaign audience as a protester was being escorted out. Wallace called his protesters “commies.” Trump called his protesters “animals,” the same word he uses for terrorists. When comparing the Wallace and Trump campaign styles last year, Tom Turnipseed, the Wallace ’68 campaign manager, told me, “They are a lot alike.” He said they both used “the politics of fear”—“You know, it’s like you gotta be afraid. You know, the black folks are taking over. And, you know, Trump, the Mexicans are coming. The Chinese are going to get you.”

After the rioting at the Democratic convention, Wallace surged in the polls, pulling more voters from Nixon than Humphrey. “I don’t talk about race or segregation anymore,” Wallace said in September. “We’re talking about law and order.” Nixon became the “law and order” candidate, as have all Republican presidential candidates since then. Nixon chose a running mate who sounded like Wallace and Trump. “If you’ve seen one slum you’ve seen them all,” said Spiro Agnew. He called a Japanese reporter a “fat Jap.” He called Humphrey “squishy soft on communism.”

Candidate Trump’s insistence that he knew “more about ISIS than the generals do” and that he had a secret plan to defeat ISIS was modelled on candidate Nixon’s 1968 secret plan to end the Vietnam War, a war that the Nixon-Ford administration did not end until 1975.

In an election that Nixon won by less than 1 percent of the vote, it is likely that Nixon would not have won without Roger Ailes and the innovative media strategy he helped create for the campaign. As a campaign media strategist, Ailes helped elect two more Republican presidents, Ronald Reagan and George H.W. Bush. As the president of Fox News, Ailes helped elect two more Republican presidents, George W. Bush and Donald Trump. We have reason to wonder who would be president today if Richard Nixon had not lured Ailes into presidential politics in 1968.

The last liberal standing on a Republican convention stage was New York City Mayor John Lindsay in 1968.  In one of the most poignant moments of that year, after failing to get the vice presidential nomination himself, Lindsay was forced into the humiliating role of seconding the nomination of Spiro Agnew. The cleansing of the parties picked up speed after that and was complete by the end of the century.

When the parties agree on nothing, it’s easier to think of the other party as “the enemy,” a term President Trump has used for his opponents. It’s easier to call peaceful protesters “animals.”  By the end of the ’70s, politicians like George Wallace, Spiro Agnew, and Richard Nixon seemed like an extinct breed. Now they seem ahead of their time.