When Michael Flynn signed on with Donald Trump's presidential campaign despite not really knowing the candidate personally, the reason seemed obvious: Flynn was pretty much the only retired senior military officer who publicly supported Trump. The two also shared a certain outlook on the world, particularly a penchant for insane conspiracy theories of both the anti-Muslim and anti-Democrat variety. But it turned out that Flynn shares something else with his ex-boss: a deep personal corruption, which made him a perfect candidate for entry to the Trump inner circle.

That characteristic of the president's orbit — that so many of those around him are in one way or another versions of himself — is providing the fuel for special counsel Robert Mueller's investigation, which may have started with Russia's involvement in the 2016 campaign, but is going to reach much farther. And lots of people around Trump are going to find themselves in big trouble.

Let's start with Flynn, who is looking more and more like pretty much the last person who should ever have been near a classified briefing. Flynn was tossed from the White House after a brief tenure as national security adviser after lying about his contacts with Russian officials, but as time went on, we learned of even more alarming things he had done. Just before Trump's inauguration, as he was working on the transition with Obama administration officials, Flynn reportedly stopped an American military operation against ISIS that the Turkish government opposed — without informing anyone that Turkey had paid him half a million dollars to represent their interests (he later retroactively registered as a foreign agent).

And this week we learned that during the transition Flynn pushed for the incoming administration to promote a private-sector plan to build nuclear reactors across the Middle East — and you guessed it, he was reportedly being paid by the companies backing the plan.

In other words, Flynn saw serving in the Trump administration as a way to cash in. Which makes him a lot like the president himself, for whom "conflict of interest" is just another way to say "profit opportunity."

Robert Mueller is taking a very, very close look at Flynn's activities. And he's also examining Flynn's son, Michael Jr., who served as his father's chief of staff at the elder Flynn's consulting firm and worked on the presidential transition.

Then of course there's Donald Trump Jr., who set up that fateful meeting with a group of Russians with connections to the Kremlin, then lied about it, claiming that it only concerned adoptions of Russian children. His current story is that he was hoping they'd have dirt on Hillary Clinton but it turns out they didn't, meaning he tried and failed to collude with Moscow.

That's not to mention the other attendees at that meeting, then-campaign chairman Paul Manafort, who has a whole web of shady Eastern European goings-on in his background, and presidential son-in-law Jared Kushner, whose family has been busy using their connections to the president to try to drum up Chinese cash for their overextended real estate holdings. Some of Trump's lawyers have reportedly pressed for Kushner to leave the White House, believing that his exposure to the Russia investigation poses too great a risk for the president.

Then there are the other characters who have been involved in Trump's various dealings over the years with the Russian oligarchs and mobsters who have reportedly rained hundreds of millions of dollars down on him. You've got his "personal lawyer" Michael Cohen, who was trying to negotiate a deal for a Trump Tower in Moscow while the campaign was going on, and Felix Sater, the criminal and occasional Trump partner who connected him to all kinds of Russian money. Those are just some of the ones we already know about.

The point is, scandals like these are never confined to one wrongdoer. It may even be possible that there was no collusion between anyone on the Trump campaign and anyone in Russia (much as I doubt it), but once you start tugging on all these threads, who knows what will come slithering out. Mueller has the authority and the resources to pursue any criminal activity he finds evidence of, even if it doesn't directly involve Russia's effort to help Donald Trump get elected, and with this group of upstanding citizens — from the president on down — the chances that nothing nefarious will emerge are so tiny you'd need an electron microscope to see them.

According to a report Wednesday by Mike Allen of Axios, "Behind the scenes in the West Wing, President Trump continues to rant and brood about former FBI Director Jim Comey and the Russia investigation that got him fired," and "the president's friends are most worried about Mueller digging into past business deals." That is indeed what they should be worried about.

If Trump was an honest businessman who surrounded himself with only people of integrity and character throughout his career, he wouldn't have much to worry about. But he has always attracted people whose morals were flexible and whose most profound question was "What's in it for me?", whether it was in real estate or as a candidate and now president. And with the special counsel digging around, there are probably a whole lot of Trump associates lying in bed at night worrying about whether they're going to get caught.