Donald Trump loves nicknames. Over the year-long course of his bombastic campaigning he's come up with a bunch of 'em for various opponents: Lyin' Ted, Little Marco, Crooked Hillary, Low-energy Jeb and his latest, Goofy Elizabeth and Crazy Bernie. So it's time we slap a label on Trump himself: Broke Donald.

And why Broke Donald? Because his refusal to release his tax returns raises major suspicion that he's either insolvent and/or involved in business transactions or investments that portray him in a negative light. Is there another explanation for why he refuses to hand them over until at least after the election, if at all? He claims he "can't" release them because he's in the middle of an audit. But as I wrote back in March, even the IRS states that the decision to release his tax returns is Trump's and only Trump's.

Every presidential nominee for the past forty years has released tax returns before the election. So Trump's refusal raises the billion-dollar question, what's he hiding? Is he broke? Will the returns show low income? Low tax rate? Massive debt? Business losses? Do the returns show an embarrassingly low amount of charitable contributions? And to whom he's contributed to, or not? For example, has he not supported veterans as he's claimed? Do the returns show questionable deductions and/or offshore investments and shelters? Something even worse? As the GOP's 2012 nominee Mitt Romney suggested Tuesday, is there a "bombshell" in there?

Contrary to Trump's claim that "tax returns show very, very little," these official documents actually show quite a lot, and provide an official window into an individual's true financial standing. So maybe Trump's insistence that they remain private is because they're the house of cards that could bring down the house of Trump.

And there's the problem. For an individual who's anchored his entire narrative to his "huge" wealth, perhaps those tax returns would be a devastating blow to the Trump mystique and brand. Imagine what life would be like for Trump if it appeared that he wasn't worth the $10-billion he's claimed? If he couldn't brag about his success and those billions. Shielding his tax returns from the public certainly allows him to continue his relentless trumped-up self-aggrandizing.

Let's be clear: it's not been the American people who've entered Trump's personal wealth into the campaign as the candidate's primary political asset. It's been Trump himself who's consistently claimed for a year now that his personal fortune and business success are his core presidential calling cards. Which is why verifying those claims should be an essential part of the vetting process.

Hillary Clinton should embrace "Broke Donald" and run with it. She should define the presumptive Republican nominee as a financial fraud. She should attack him where it'd hurt the most. The one button that when pushed would rattle Trump like no other. His wealth is how he defines himself. Attack the money and you attack the man. And it's what she should do non-stop until November. It'd keep her on offense and him on defense.

Imagine the following ad: "Broke Donald. Refuses to release his tax returns. What's he hiding? Is his "huge" wealth just a myth? Is Donald Trump a financial fraud? I'm Hillary Clinton...and I approved this ad..."