Thanks mostly to Donald Trump, American politics is more in flux than it has been since the Solid South abandoned the Democratic Party in the wake of the civil rights revolution.

The Republican Party — once in thrall to groups like the Moral Majority and the Christian Coalition — has nominated a thrice-married former reality-show host whose grasp of the Bible needs to be graded on a curve. During Monday night’s debate, Trump again repudiated such bedrock GOP principles as free trade and fidelity to NATO.

Hillary Clinton, blessed with the support of large segments of the moderate Republican foreign policy establishment, may be the most hawkish Democratic presidential nominee since Hubert Humphrey in 1968. Though, in fairness, the Al Gore of 2000 probably comes close.

The political map is in the midst of its biggest rewrite since 1996 when Bill Clinton swept such now safe GOP bastions as Louisiana, Arkansas, Missouri, Kentucky, Tennessee and West Virginia. It is weird when the 2016 action pivots around Pennsylvania (which last was carried by the Republicans in 1988) and North Carolina (which has only gone Democratic once in the last nine elections).

That’s why traditionalists, regardless of party or ideology, should have been thrilled when Hillary during the debate emphasized a Democratic theme older than even FDR’s theme song, “Happy Days Are Here Again.” In a topsy-turvy political world, there is only one constant — the Democrats will always denounce Republican “trickle-down economics.”

Gussied up a bit

Clinton gussied it up a bit, calling it “trumped-up trickle-down,” in an obviously rehearsed line that she repeated twice for emphasis. As the former New York senator put it: “Trickle-down did not work. It got us into the mess we were in, in 2008 and 2009. Slashing taxes on the wealthy hasn’t worked.”

The expression — “trickle-down economics” — sounds like it was lifted from another era. You can almost see a farm family at supper spilling a pitcher of milk and their cat lapping it up from the floor.

William Safire, the late New York Times columnist and legendary political linguist, traced the concept back to populist William Jennings Bryan’s “Cross of Gold” speech” that electrified the 1896 Democratic convention. Bryan denounced conservatives who believed that if “you legislate to make the well-to-do prosperous, their prosperity will leak through on those below.”

But it took another great Democratic orator, Franklin D. Roosevelt, to get the wording right. In an October 1932 campaign address in Detroit, in the depth of the Depression, Roosevelt ridiculed those who believe that “if we make the rich richer, somehow they will let part of their prosperity trickle down on the rest of us.”

Just because FDR said it doesn’t mean that a line will endure as a staple of Democratic oratory for eight decades. You don’t hear Democrats today — especially not Hillary Clinton — denounce the “economic royalists” whom Roosevelt excoriated in his 1936 re-election campaign.

But somehow “trickle-down” dripped its way onto the texts of Democratic Party speechwriters. Part of its appeal was the homeyness of the imagery and part of it was its often apt description of GOP economic proposals.

Campaigning on behalf of the Democratic ticket in October 1952, Harry Truman lamented that during the 1920s “many short-sighted people honestly believed that, if big business got along well, enough wealth and income would trickle down to the rest of the population to keep the system going.”

‘A rising tide’

The expression might have died out during the Kennedy years when the mantra was “a rising tide lifts all boats.” But first Richard Nixon and then, especially, Ronald Reagan brought “trickle-down” back into the Democratic lexicon.

Probably the architect of the revival of “trickle-down” was David Stockman, Reagan’s first OMB director. In an exceptionally candid series of 1981 interviews with Bill Greider for the Atlantic Monthly, Stockman confessed that the unrealistic budget estimates of “supply side” economics were needed to pass Reagan’s tax cuts.

As Stockman memorably put it, “It’s kind of hard to sell ‘trickle-down’ so the supply side formula was the only way to get tax policy that was really ‘trickle-down.'”

Bill Clinton’s 1992 presidential campaign — which was shaped as the belated Democratic response to Reaganism — regularly attacked “trickle-down economics.” In his first debate with George H.W. Bush and Ross Perot, the Arkansas governor argued that the Reagan tax cuts failed to “trickle down” to the middle class.

In fact, during that 1992 campaign, Hillary Clinton joined in the “trickle-down” chorus. Campaigning on her own in Florida in late August, Hillary told a crowd of mostly women at the Tampa Convention Center that trickle-down economics hadn’t worked under either Reagan or Bush.

At the beginning of her current race for the White House, Hillary harked back to Reagan in her first major economic speech in July 2015. “For 35 years,” she said, “Republicans have argued that if we give more wealth to those at [the] top by cutting their taxes … it will trickle down to everyone else. Yet every time they have a chance to try that approach, it explodes the national debt, concentrates wealth even more and does practically nothing to help hard-working Americans.”

Even though “trickle-down” didn’t make it into Clinton’s acceptance speech in Philadelphia, she brought it back to center stage Monday night. It was just another moment in the spotlight for the unsinkable epithet that Democrats have used to denounce Herbert Hoover, Ronald Reagan and now Donald Trump.