The impeachment trial of former President Donald Trump in the U.S. Senate revealed curious historical parallels between today’s Republican Party and the Democratic Party of half a century ago, which explains also why the Republicans in their current state are a party unfit to govern.

On the south side of West 11 Street in New York City’s Greenwich Village, a row of a dozen 19th century Greek Revival townhouses is interrupted at No. 18 by a modern house. In March 1970, the original building on that site was destroyed by a powerful explosion. Members of a paramilitary group Weather Underground were making bombs in its basement when one of them accidentally went off. Three Weathermen died.

The late 1960s and the early 1970s were the age of domestic left-wing terrorism. There were the Black Panthers, the Symbionese Liberation Army, the FALN, and others.

Besides the violent fringe, there were various radical organizations ready to take to the streets, as they did in 1968, during the Democratic National Convention in Chicago.

The terrorists and the radicals were not part of the Democratic Party and were mostly opposed to the entire American establishment. But there were enough sympathizers on the left of the Democrats to pull the party away from the American mainstream and to make it difficult for Democratic executives to govern. Lyndon Johnson chose not to run in 1968, Richard Nixon crushed George McGovern 520-17 in the electoral college in that year’s presidential election and Jimmy Carter, despite having solid post-Watergate majorities in Congress, proved a remarkably ineffectual president.

On Carter’s watch America suffered a series of humiliating defeats. It seemed to have entered a terminal decline and the communists in the Kremlin were rubbing their hands in anticipation of imminent victory in the Cold War.

The Republicans under Ronald Reagan restored American leadership, which was largely the work of competent men such as James Baker, Caspar Weinberger and George Shultz, who died last week at the ripe age of 100. They rebuilt the American economy, bolstered the Western alliance, restructured the military and successfully stood up to Moscow, eventually sending the Evil Empire onto the dustheap of history.

These men were conservative and they were realists. Yet, the drift of the Republican Party into lunacy also began with Reagan. It started innocently enough with an attack on bloated government finances and taxation, while encouraging evangelicals and other religious people to get involved in politics to fight the secular foundations of the American democracy.

Like the radicalized Democrats in the 1960s, the radicalized Republicans began losing their ability to govern effectively under the first George Bush, who was undone by his attempt to repair federal finances with — horrors — a modest tax increase. Then, the two terms of his son’s presidency would have been a study in grotesque misgovernment but for the four years of the Trump administration.

A president elected by a minority of votes, George W. Bush rushed in with a radical agenda, opening a giant structural budget gap with his tax cuts. His government was asleep at the switch before the 9/11 terrorist attacks and when they did happen unleashed its misbegotten Global War on Terror. He sent the US military — built by Weinberger for limited surgical strikes and swift police action — into two wars of occupation. Both are still going on two decades later, even though they have been lost long ago, and the embittered military personnel, returning home from the battlefield, are swelling the ranks of right-wing radicals just as the World War I German and Austrian veterans swelled the ranks of the Nazi party.

Bush’s Federal Emergency Management Agency showed the world how badly an under-resourced government agency staffed with underpaid mediocrities could mishandle an emergency situation when a storm destroyed New Orleans.

Finally, Bush’s stint as president culminated in the worst financial debacle since the Depression. The global financial system came close to collapse and the US auto industry — at the time the world’s largest — was nearly wiped out. Both were saved by a timely intervention of the incoming Obama administration.

The Democrats never had a radical leftist president to represent them during their radical stage. McGovern lost but even he was no Tom Hayden or Bill Ayers. In Trump, the right-wing radical movement finally had a representative in the White House — albeit also elected by a minority of voters.

Trump’s impeachment trial revealed remarkable parallels between today’s right-wing radicals and the left-wing radicals of yore. What we saw in the video footage from the January 6 riot at the Capitol were the full-grown adepts of the radical ideology first planted by Reagan — libertarians, anti-taxers, religious zealots, and of course plain old terrorists. What they shared with the Weathermen and other left-wing radicals was hatred of the United States.

What we also saw in the chambers was a Republican Party overtaken by radicals and by the radical propensity for magical thinking. Forget governing — they are incapable of convicting a man who sent a violent mob to attack them. There was an added piquancy in the fact that all but seven Republican senators voted to acquit Trump on the day after Abraham Lincoln’s birthday, kind of symbolically signing the death warrant for the great man’s party.

The Democrats first began to move toward realism under Bill Clinton. Democratic governments have been characterized by stability and a firm hand on the rudder. Biden has given a strong signal that he will return the country to normalcy. A majority of Americans — who have been refusing to vote for a Republican president in five of the past six elections — seem to approve of Biden and his policies a lot more than they ever did of Trump.