There are several ways to break down the trends. Eisenhower's Administration in retrospect is a model of "moderate" Republicanism, although he gets more credit for a peaceful foreign policy than he deserves. His "tripwire/massive retaliation" nuclear policy was a genuinely high-risk position. And he actually threatened to use nuclear weapons against North Korea.
The Goldwater candidacy in 1964 was a major marker in the process. But it did not yet define the national party. The Nixon Administration was path-breaking in authoritarian usage of Presidential power. But his nuclear arms-control policies, his diplomatic bridge-building to China, and even his Vietnamization policy diverged from the positions that the Goldwater right and the John Birch Society types favored. Nixon used wage-and-price controls to limit inflation, and even proposed a limited form of national health insurance that was arguably more comprehensive than "Obamacare".
Jerry Ford established a major precedent for Presidential impunity for serious crimes by issuing a blanket pardon to Richard Nixon. He also elevated the careers of Donald Rumsfeld and Dick Cheney, who have the dubious distinction of being two of the most destructive characters in American politics.
The Presidential candidacy of Ronald Reagan in 1980 was a decisive turning point for the Republican Party, representing a convergence of neoliberal market fundamentalism, a general endorsement of hard right politics, and focused authoritarianism. The Iran-Contra affair was itself a real Constitutional crisis, which the Republicans took in stride and the Democrats didn't dispute as actively as they should have. Old Man Bush expanded Republican official impunity by pardoning Iran-Contra criminals. And Bush's own actual role in the possible (I would say likely) 1980 "October Surprise" dealings with Iran.
The fall of the Warsaw Pact and the decline in the fall of the USSR changed the international picture so dramatically that it makes it hard to describe the nature of the continuity and change during the Bush-Quayle Administration. They initiated a serious of closing military bases that would have seemed like a pacifist dream a few years before. But they also conducted the first Gulf War, which in retrospect was a fateful escalation toward what became the current Middle East situation. In general, the Bush family ties to the Saudi monarchy that Craig Unger ably described in House of Bush, House of Saud (2004) have had serious negative consequences for US foreign policy and the well-being of ordinary people in the Middle East.
But since the 1994 midterms elections which marked the so-called Gingrich Revolution, the radicalization of the Republican Party has seemingly proceeded steadily. They keep getting more authoritarian, more crassly oligarchic and rightwing, more bitterly divisive, and generally more fanatical and sleazy. And this is definitely not a case of Both Sides Do It. Nothing remotely similar has happened on the Democratic side. In fact, one of the most important defining facts of American politics since 1994 has been the asymmetric polarization beteen the two political parties.
But I always want to give Richard Nixon his due in this process. Henry Steele Commager (1902 – March 2, 1998) was a major liberal American historian in the 20th century. He was a classic "Cold War liberal" in the Truman years, very much a supporter of Truman's containment policy against the Soviet Union. During the 1960s, he became an activist critic of the Vietnam War and actually developed a sometimes radical critique of American politics based on his understanding of how Cold War foreign policy was undermining the liberal principles on which the US government and Constitution were based. In other words, an imminent critique founded on his focus on the democratic elements of classical liberal political theory.
A collection of essays published in 1975 under the title The Defeat of America features that perspective, in particular with relation to the Nixon Administration. Including the essay from which the title of the book is derived, which originally appeared in the New York Review of Books (10/05/1972 issue). He had this to say about how Nixon was undermining the system (text from the book):
Basic to an understanding of the usurpations, duplicities, and irresponsibilities of the Nixon era, then, is paranoia, which has a life of its own, and which still lingers on - even after the "end" of the [Vietnam] war and the rapprochement with China - polluting the moral and intellectual atmosphere of the country. Certainly there is little evidence that Mr. Nixon or his underlings think the new relationship with the Soviet Union and China justifies the mitigation of their own paranoia about "national security," or their conviction that any attack upon official policy is itself a potential threat to security. How else explain the vindictiveness of the prosecution of Daniel Ellsberg and the readiness to subvert justice in that prosecution; how else explain the political skulduggery that persisted long after the 1972 election, the persistent use of the FBI and the CIA for political purposes, the readiness to employ provocative agents, the contumacious boast at the POW dinner that reliance on secrecy, even useless secrecy, would go on and on; how else explain the determination to bomb Cambodia back to the Stone Age? ...It is noteworthy that Commager viewed the approach of Nixon to government and politics as an attempted "revolution". Or, as he puts it, "an unconstitutional revolution"; Commager would later describe Nixon's impeachment as a legal and constitutional revolution. But he viewed the Nixon version as being revolutionary in the sense of revolutionary dictatorship as in the Terror during the French Revolution, which both classical liberal and conservative political theory regard as a cautionary tale of arbitrary excess. And which Edmund Burke, a godfather of modern reactionary political thought, used as his prime bogeyman.
Is the crisis of the present so imperative that it requires an unconstitutional revolution - requires, that is, abandoning the separation of powers, discarding limitations on the executive authority, weakening legislative control of the purse, repealing the Bill of Rights, subverting the traditional rule of law, and covering with a fog of secrecy the operations of government? Clearly Mr. Nixon and a good many of his followers think that it is. Now we are back with the phobia about communism and paranoia about national security. [my emphasis]
It was from reading Commager among others that I first became aware of the pragmatic criticism that a big problem for US foreign policy has been a failure to understand revolutionary processes, even losing sight of the revolutionary traditions in the US itself. That is still true today, for both parties. But the Republicans have long since become accustomed to thinking and talking in terms of revolution, or "unconstitutional revolution" in Commager's somewhat awkward phrase: the Reagan Revolution, the Gingrich Revolution, the Tea Party, today's armed protests by Trump cultists in favor of unrestricted spread of the COVID-19 virus, the lunatics of QAnon, even Alex Jones' advocacy of murdering and eating his neighbors. (On the latter, see: Oliver O'Connell, Alex Jones says he'd kill and cook his neighbours to feed his kids Independent 05/01/2020. Though I don't recall ever hearing that cannabalism was a feature of the French Terror.)
Meanwhile, on the "other side of the aisle," when Bernie Sanders talked about having a "revolution" involving broader voter participation and national health insurance of the type that is standard in European democracies, conservative Democrats professed to see vision of guillotine blades dropping. A good illustration of how asymetric partisan polarization works in American politics.
But going back to Tricky Dick, his administration established a practice of authoritarian illegality that took deep roots in the Republican Party. It also established a defensive mentality among Nixon's hardline fans that the law should be just another political tool in the partisan war. One used only by Republicans, of course. The rabid allegiance of Trump's cult followers is the most recent flowering of that attitude. It won't be the last. And it won't be eliminated by Democrats chasing a chimera of Bipartisan harmony with today's extremist Republican Party.
A more radical critic of the Nixon Administration, the Frankfurt School philosopher Herbert Marcuse, whose perspective was not restricted to the liberal political tradition, formulated this view of the situation at the time of Commager's observations quoted above (Countervrevolution and Revolt, 1972):
The Western world has reached a new stage of development: now, the defense of the capitalist system requires the organization of counterrevolution at home and abroad. ...For anyone who is wondering, by "world-historical revolution" Marcuse had something more drastic in mind than simply national health insurance. Which, as I mentioned, was an entirely respectable idea in 1972, even among some senior Republicans, and not seen as remotely "revolutionary" in the then-mainstream of both parties.
The counterrevolution is largely preventive and, in the Western world, altogether preventive. Here, there is no recent revolution to be undone, and there is none in the offing. And yet, fear of revolution which creates the common interest links the various stages and forms of the counterrevolution. It runs the whole gamut from parliamentary democracy via the police state to open dictatorship. Capitalism reorganizes itself to meet the threat of a revolution which would be the most radical of all historical revolutions. It would be the first truly world-historical revolution. [my emphasis in bold]
