There’s a common thread that stretches forward from Donald Trump’s financial scandals of the 1980s to his damning phone call with the president of Ukraine.

It’s the self-dealing.

Wherever he was, whatever his title, the president has used the powers at his disposal to enrich or otherwise benefit himself, regardless of what law, fiduciary duty or oath of office bound him to do.

Trump ran his campaign in 2016 on a single premise: greed. (Okay, two premises: greed and racism.) He boasted to his fans about his (inflated) wealth and gilded lifestyle, both products of clever deployments of his avarice. It was a trait he promised, paradoxically, that he’d apply more altruistically once elected.

“My whole life I’ve been greedy, greedy, greedy,” he said at a January 2016 rally. “I’ve grabbed all the money I could get. I’m so greedy. But now I want to be greedy for the United States. I want to grab all that money. I’m going to be greedy for the United States.”

His track record suggested that would be unlikely, perhaps impossible — in part because his life has always been about blurring lines between personal gain and professional or legal responsibilities.

This was the case when the Trump family set up a shell company called All County Building Supply & Maintenance in the early 1990s, to pretend to purchase boilers, cleaning supplies and other building equipment from (real) vendors. This middleman, which existed only on paper, then “resold” everything at an inflated price to the Trump Organization. The purpose of the shell company was to allow Trump’s father, Fred, to transfer huge cash gifts to his children as though they were ordinary business transactions. This helped the Trump family evade a 55 percent estate tax, as the New York Times reported last year.

It was also the case from the 1980s through the past presidential campaign, as Trump siphoned funds from his charity for his personal benefit. He used Trump Foundation money to settle legal disputes involving his for-profit companies, to renovate a fountain outside one of his hotels and to buy enormous portraits of himself, as my Post colleague David A. Fahrenthold documented.

It was likewise the case when his once-publicly-traded company, Trump Hotels & Casino Resorts, inflated financial results in a way that the Securities and Exchange Commission said served to mislead investors. And also when his private company allegedly provided false sales figures for real estate developments in Mexico, Panama, Toronto and New York.

And so on.

Such cases repeatedly showed that Trump had no problem draining money from bondholders, investors or tax coffers if he thought he could get away with it. They also illustrated exactly how he might govern as president: in his own interest.

Trump’s supporters shrugged off his refusal to divest from his business interests, arguing that it didn’t matter if he continued to make money while president so long as he still did right by the country. But we knew at some point he’d have to decide between a policy that benefited the country and one that benefited himself.

And we knew which choice he’d make.

So it was no surprise that his administration abruptly canceled the planned relocation of the FBI headquarters, which might have allowed the existing site to be redeveloped into a hotel that would compete with the nearby Trump International Hotel.

Or that foreign leaders and business executives have patronized this and other Trump properties around the world, in a transparent attempt to influence U.S. policy on aid, arms deals and merger approvals. In fact, during their now-infamous July 25 call, the Ukrainian president made sure to note a recent stay at a Trump property in New York.

It’s likewise shocking, but not altogether surprising, that military personnel have had unnecessary layovers at Trump’s Scottish resort. Or that Vice President Pence stayed at the president’s Irish resort while attending meetings 180 miles away. Or that the Secret Service has spent hundreds of thousands of dollars at a single Trump hotel — in Washington.

This is exactly the kind of stuff that worried those who wrung their hands about his shady, self-dealing, private-sector past.

Moreover, given Trump’s rampant small-time grifting in public, it seemed impossible to imagine he wouldn’t go after bigger fish in private — including, say, extorting a foreign power into smearing a political rival.

Trump maintains that his call with the Ukrainian president was “perfect.” And, hey, maybe he genuinely believes this. Indeed, the best defense you can give for Trump’s actions is that after all these years he has become incapable of telling the difference between his own interests and anyone else’s — and by extension, what it means to be “greedy” for himself vs. “greedy” for the United States.

Perhaps for Trump, as for France’s Louis XIV, “l’état, c’est moi.”

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