For decades, conservatives labored to make their movement more humane. Ronald Reagan put a jovial face on conservative policies — more Dale Carnegie than Ayn Rand; George H.W. Bush promised a "kinder, gentler" tenure; George W. Bush ran on "compassionate conservatism." As a progressive, I opposed many of their specific proposals. But as a country, we benefited from a debate between competing ideas — liberal and conservative — on how to soften the hard edges of American life and create a more inclusive country.

That was then. Today, we are living the Politics of Mean. In the Trump presidency, with its daily acts of cruelty, punching down is a feature, not a bug. And the only thing more disquieting than a president who practices the Politics of Mean are the voters who celebrate it.

President Trump's decision to put some 700,000 "dreamers" in limbo, his snarling statement that athletes protesting policing abuses are "sons of bitches," his opposition to bipartisan efforts to maintain health coverage for low-income families, his feud with a Gold Star widow are all recent examples — not of conservative policies — but of a basic nastiness. Hundreds of thousands of Puerto Ricans still lack water, most are without electricity, leptospirosis is spreading, and Trump talks about withdrawing federal aid and belittles local leaders. Nine months into his presidency, Trump is not even paying lip service to the compassionate ideals — such as improving low-performing schools or combating homelessness — that previous Republican presidents pursued.

Trump always will be Trump. He won the White House on a campaign of insults and taunts, urging rally attendees to punch protesters and threatening to jail his opponent. We have known who he is. But what is his presidency saying about the rest of us?

Since Trump's victory, his meanness has been infectious. We have seen it in neo-Nazis marching in Charlottesville and elsewhere, students chanting "build that wall" at Hispanic peers, and a rise of racial epithets and anti-Semitic graffiti on college campuses. Puerto Rico, again, provides a current example. As The Post's Jenna Johnson recently reported, countless Trump supporters — including some in Texas, who themselves took Federal Emergency Management Agency aid after Hurricane Harvey — back the president's proposal to limit aid to Puerto Rico and believe that fellow Americans there should "fix their own country up."

These sentiments were present in dark corners of our country before Trump; they will remain after he leaves. But there is little question that Trump promotes such meanness. He is unique among presidents in using the “bully pulpit” not to suppress such tendencies but to enflame them.

Trump's core supporters will never change. But thankfully, a year after Election Day 2016, there are signs that Trump's cruelty may be wearing on a growing number of Americans. Trump's average approval ratings are at an all-time low for first-year presidents, an astonishing fact given that he is presiding over record-high stock prices and low unemployment numbers. A handful of Republican senators — most recently, Tennessee's Bob Corker — have started to speak out against him. And Democratic pollster Geoff Garin reported last week that in his focus groups, for the first time, "I am hearing Trump voters talk much more often about Trump's meanness and lack of compassion."

At this moment of truth, we need leaders to confront the meanness of Trumpism. Hillary Clinton has relentlessly done so, notwithstanding the ridicule she has suffered for it. In recent days, three of the five other major-party nominees for president this century — George W. Bush, John McCain and Barack Obama — have also spoken out. McCain declaimed a "half-baked, spurious nationalism." Bush called out a "discourse degraded by casual cruelty." Obama urged Americans to reject "a politics of division" and "a politics of fear." All three speeches were powerful.

But due to some mix of custom and caution, all three stopped short of mentioning Trump by name — allowing the White House to deny that Bush and Obama were rebuking the president. Is Trump — like a certain fictional character, popular at Halloween time — “he who must not be named”? If these powerful people cannot be clear about the target of their criticism, should the rest of us be afraid to do so?

In the season of witches and wizards, Harry Potter does indeed have an answer. In the books, the wise Dumbledore tells Harry to reject the custom of refusing to speak the name of the one spreading fear and hate, saying: "Always use the proper name for things. Fear of a name increases fear of the thing itself."

McCain, Bush, Obama and Clinton — joined by the other major-party nominees of this generation (Mitt Romney, Al Gore and John F. Kerry) — should step up their calls on the American people to reject hatred, division, nativism and nastiness. They should lead us in ending the Politics of Mean. And they should not fear to speak the name of the man — Donald Trump — who has visited it upon us.