As a Donald Trump victory became clear Tuesday night, the ghost of Herbert Hoover paid a visit to Trump’s election night party in New York.

In the Fox News coverage playing on screens in the ballroom, Megyn Kelly turned to Karl Rove. “It didn’t happen under Reagan or the Bushes. When was the last time a Republican president had a Republican Congress?”

“1928,” Rove answered.

“Incredible,” Kelly said.

Yes, quite: Republicans actually had unified control for four years under George W. Bush, and for two years under Dwight Eisenhower, as Rove amended when I followed up with him.

Expecting a celebration, The Washington Post’s Dana Milbank wrote a letter to his daughter to help her cope with Hillary Clinton’s electoral loss. (Adriana Usero/The Washington Post)

But the 1928 comparison is instructive. It’s the last time a Republican president enjoyed anything like the majority Trump will have, particularly in the House.

And how did that work out for them?

Hoover took over in a time of general prosperity but stagnant wages and vast income inequality. Populists in Congress proposed dramatic increases in tariffs to help the struggling agricultural sector, the equivalent of today’s beleaguered blue-collar workers.

The proposal divided Republicans in Congress and Hoover before they produced the 1930 Smoot-Hawley Tariff Act, setting off retaliation, freezing international trade, contributing to the Great Depression and accelerating a ruinous cycle of nationalism around the world.

Hoover’s ghost should haunt the GOP right now. A populist, protectionist president has come to power at a time of long-depressed wages and vast inequality. He threatens to implement tariffs of 45 percent against China and 35 percent against Mexico, and he’s about to collide with free-traders and pro-business interests in his own party.

If they jettison Trump’s agenda and proceed with business as usual, they risk inflaming Trump’s already-furious followers. If they do what Trump has promised, there will be chaos as they pursue what amounts to a mission impossible: enacting a huge tax cut, making enormous spending increases on infrastructure and the military and cutting the debt in half — all without touching Social Security and Medicare.

And they’ll be without a mutual foil to unite them. President Obama will be out of office, Hillary Clinton defeated, Harry Reid retired. With unified control, Republicans now own every issue — health care, the economy, national security — and Democrats, who narrowly won the popular vote and are supported by exit polls showing tepid support for many of Trump’s policy priorities, have little incentive to cooperate.

Some early signs show Trump won’t hesitate to disappoint supporters, including his statement Friday that, after talking with Obama, he no longer favors repealing all of Obamacare.

Drain the swamp? Trump has packed his transition team with a who’s who of the K Street lobbying trade, according to Politico. Among those in charge of staffing the new administration are people who have lobbied for or represented Altria, Visa, Anthem, Coca-Cola, General Electric, HSBC, Pfizer, PhRMA, United Airlines, Southern Company, Dow Chemical, Rosemont Copper Company, Boeing, Duke Energy and Nucor.

My colleague Catherine Ho reports that Trump’s win “is likely to be a boon to the lobbying business,” as businesses try to counteract the uncertainty with more lobbyists.

The Trump-proposed ban on Muslims entering the country? As The Post’s Jose A. DelReal reported, the Trump campaign removed that policy’s web page Thursday, then restored it after the reporter’s inquiries.

That wall on the Mexican border? “Going to take a while,” Trump lieutenant Rudy Giuliani said Thursday, suggesting “he can do it by executive order by just reprogramming money within the immigration service.”

“Reprogramming” money away from . . . deportation? Truly building the wall would cost hundreds of billions of dollars and require approval from Congress.

The “lock her up” crowd may also be disappointed. Chris Christie said “politics are over now.”

On that same question, however, Giuliani said prosecuting Clinton would be “a presidential decision” — an extraordinary departure from the American tradition of removing the president from prosecutorial decisions, particularly since President Nixon tried to block the Justice Department’s Watergate probe in 1973.

The Trump transition sounded another Nixonian note when Trump surrogate Omarosa Manigault told a conservative website that Trump is keeping an enemies list.

The conflicting signals suggest Trump himself hasn’t settled on his course. His gracious victory speech was about reaching out to the opposition, but Breitbart News, whose once and future leader ran the campaign, has been whipping up racial fears (“Shock Video Shows White Man Viciously Beaten in Chicago After Election”).

On Thursday night, the president-elect tweeted that “professional protesters, incited by the media, are protesting. Very unfair!” Friday morning he reconsidered: “Love the fact that the small groups of protesters last night have passion for our great country. We will all come together and be proud!”

Trump’s internal tension is understandable. He can leave supporters disillusioned, or he can keep his promises — and send us all back to 1928.

Twitter: @Milbank

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