(CNN) On Tuesday morning, President Donald Trump tweeted this: "For the record, I have no financial interests in Saudi Arabia (or Russia, for that matter). Any suggestion that I have is just more FAKE NEWS (of which there is plenty)!"

Which, maybe!

There's simply no way to check whether Trump's claim is true because he continues to be the first president in the modern era to not release any of his tax returns, returns that would show his financial relationships (if any!) with Saudi Arabia.

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(Sidebar: While there are no Trump properties in Saudi Arabia, Trump did say this about the Saudis on the 2016 campaign trail: "I get along great with all of them. They buy apartments from me. They spend $40 million, $50 million. Am I supposed to dislike them? I like them very much!")

This is a re-occurring theme of the Trump presidency: He makes a claim regarding his financial holdings -- or finances more generally -- that simply cannot be verified (or debunked) because we have an incredibly limited window into his actual finances.

A few examples:

* Last fall, as part of his rollout of his tax cut plan, Trump said this (bolding is mine): "Our framework includes our explicit commitment that tax reform will protect low-income and middle-income households, not the wealthy and well-connected. They can call me all they want. It's not going to help. I'm doing the right thing, and it's not good for me. Believe me."

* In May 2017, Trump tweeted this about critics of his relationship with Russia and Russian president Vladimir Putin: "I don't know Putin, have no deals in Russia, and the haters are going crazy - yet Obama can make a deal with Iran, #1 in terror, no problem!"

In each of these situations, Trump is saying, essentially: Trust me.

The problem with that two-word assurance from Trump is that he is someone uniquely unacquainted with truth. As of early September, Trump had made more than 5,000 false or misleading claims in just over 600 days as president, according to a count being kept by the Washington Post's Fact Checker blog . (For you non-math majors out there, that's an average of more than eight false or misleading statements every single day of Trump's presidency.)

That record begs for more documentation of Trump's claims about where he has business or holdings than just his words. But, as of today, we don't have any.

Trump and his senior aides have long maintained that he can't release his tax returns because they are under audit by the IRS. This is not technically accurate. Trump could absolutely release his returns while under audit -- as Richard Nixon did as president in 1973. Trump doesn't want to release tax returns. And so he hasn't.

"The President filed an extension for his 2017 tax return, as do many Americans with complex returns," White House press secretary Sarah Sanders said on April 17 aka Tax Day. "He will file his tax return by the extension deadline of October 15, 2018." (Yes, October 15 was Monday. But no word from the White House about Trump's filing -- or any plans to release it.)

The simple fact is that Trump long ago made a calculation that the negative press he would receive by not releasing his returns would be dwarfed by the firestorm created if he did. He's willing to take these regular hits about his total lack of transparency as it relates to his own finances because he views it as less damaging that what might be come out in the returns.

What is Trump so scared of? No one really knows, although theories abound: 1) He isn't as rich as he says. 2) His wealth is largely inherited from his father (this chatter grew in the wake of a bombshell New York Times piece on Fred and Donald Trump ). 3) He didn't pay any taxes for a number of years. 4) He has loans in banks with ties to places like Russia or Saudi Arabia that would raise questions about his ability to be fully impartial as president when dealing with those countries.

It's possible, of course, that Trump simply doesn't want to release his taxes because, well, he doesn't want to do it. But, ask yourself this: If there was NOTHING problematic in his tax returns, why would he be so stubborn in his refusal to release even one year of them?