During Monday night's presidential debate, Republican nominee Donald Trump managed to turn one of the most effective attacks against Democratic nominee Hillary Clinton on himself.

It has to do with Wall Street.

When Clinton brought up Trump's debt and business dealings, she cited a report that said the real-estate mogul might owe "Wall Street and foreign banks" as much as $650 million.

Trump went on a tirade to defend himself, and the businessman made very little sense.

From The Washington Post's transcript, emphasis ours:

"The other thing, I'm extremely underleveraged. The report that said $650 [million] — which, by the way, a lot of friends of mine that know my business say, 'Boy, that's really not a lot of money.' It's not a lot of money relative to what I had.

"The buildings that were in question, they said in the same report, which was — actually, it wasn't even a bad story, to be honest with you, but the buildings are worth $3.9 billion. And the $650 [million] isn't even on that. But it's not $650 [million]. It's much less than that.

"But I could give you a list of banks, I would — if that would help you, I would give you a list of banks. These are very fine institutions, very fine banks. I could do that very quickly."

Given that Trump hasn't released his tax returns and still basically refuses to, we would love to see that list. But that's beside the point. The real point here is that Wall Street, by virtue of the developer's debts, in some ways owns Donald Trump.

Owing favors to Wall Street is an aspersion he and others have cast on Clinton many times, accusing her of coziness with the industry because of her paid speaking engagement at banks, specifically Goldman Sachs.

Of course, getting paid by Wall Street is very different from owing Wall Street money, and Clinton was right to point out that if Trump makes it to the White House, we won't know what kind of favors Trump may owe.

And not just to one bank for one speaking engagement — to a list of them for an undisclosed number of millions of dollars.

This is Clinton using a popular argument against her — that she's too cozy with finance's rich and powerful — against Trump, who has painted himself as the everyman who just happens to own a private jet with his name on it.

Trump praising banks — those "very fine institutions" in his words — couldn't have happened at a worse time. Just last week, John Stumpf, the CEO of Wells Fargo, was on Capitol Hill expressing his regret over a horrible scandal in which his employees, motivated by incentives and pressures to drum up new business, created fake accounts and opened fake credit cards for unwitting customers.

It's an easy scandal to understand. And America is very angry. Almost 90% of Americans want Stumpf to resign. The company has to pay $185 million in fines.

So now is not a good time for Trump to have to explain which banks own pieces of his empire and how many millions he owes them. And it is certainly not the time to be talking about "very fine banks."