While running for president, one of Donald Trump's businesses tried to build a big, new real estate development in Moscow and his company cozied up to Russian President Vladimir Putin’s regime to make it happen.

This has been brought to light, after years of obfuscation by Trump adherents, by a guilty plea from the president's shady former lawyer. But Trump has waved it off. “Oh, I get it! I am a very good developer,” Trump tweeted about the story, “I decide to run for president & continue to run my business — very legal & very cool, talked about it on the campaign trail....”

It may be "very legal" for a presidential nominee to cozy up to hostile foreign leaders for personal profit, but it’s not “very cool.” There is a clear conflict of interest, and it’s at least a little corrupt.

For decades, Trump had wanted a Trump Tower in Moscow. The Trump Organization hatched a plan to build Europe’s tallest building on the banks of the Moskva River. Recently published texts reveal lawyer Michael Cohen and Moscow-born ex-felon Felix Sater worked during the 2016 campaign to get close to Russian power brokers to make the project a reality.

Sater even suggested using Russia’s political corruption to advantage, arguing that Putin should be given the penthouse so other oligarchs would rush to buy apartments in the same building to be their master's neighbor.

Cohen and Sater worked on this plan through June 2016, while Trump was running for president, with Putin ally Paul Manafort as his campaign chairman. While he courted Russia for a Trump Tower, the eponymous head of the business made his case on the campaign trail for friendlier U.S. relations with Russia.

In 2015 and 2016, Russia was no longer making any effort to conceal its imperial designs. It had seized Crimea from Ukraine and was eyeing other parts of its former Soviet empire.

One need not accept the most cynical explanation, that Trump's presidential campaign was just a publicity stunt to help his businesses, or the most corrupt explanation, that he hoped to win and wanted to bend policy to enrich himself, to be troubled by what he did. The most likely explanation is that Trump was just keeping his business options open while he ran.

We have called several times on the president to sell his worldwide business holdings. This demand is usually countered by the argument that business people should not have to shed what they've spent years creating just because they want to go into politics. It's too big a penalty, too high a price.

We agree that it is a big sacrifice, and, yes, it is legal to run or own his business while being president. But not everything that is legal is prudent or ethical. Asking statesmen to make a sacrifice is hardly a novel concept. The presidency of the United States is surely a sufficiently weighty and prestigious job, and it is proper to call on its holder and all who aspire to it to make weighty sacrifices.

At the barest minimum, any presidential candidate ought to eschew pursuing new business deals in countries hostile to the United States.

That doesn’t seem too much to ask.

Trump ought to accept that it was a mistake to keep his Moscow project open after he launched the campaign. He should apologize for that and for keeping the public in the dark about it. That small gesture would indicate that he at least sees that some things that are legal for the president to do are not necessarily very cool for him to do. Not at all cool, in fact.