There's been no shortage of talk this election about Hillary Clinton's ties to Wall Street or the fact her campaign has received $21.4 million from the financial services sector.

So it was surprising when, on Wednesday, Clinton seemed like she'd been caught off guard when asked during a CNN Democratic town hall why she had accepted $675,000 in speaking fees from Goldman Sachs.

Here's the exchange between Clinton and the host, Anderson Cooper:

Cooper: "You were paid $675,000 for three speeches (to Goldman). Was that a mistake? Was that a bad error in judgment?" Clinton: "Look, I made speeches to lots of groups. I told them what I thought. I answered questions." Cooper: "But did you have to be paid $675,000?" Clinton: "Well I don’t know. That’s what they offered ... Every secretary of state I know of has done that." Cooper: "But that's usually when they're not running for office ... you must have known?" Clinton: "To be honest I wasn't — I wasn’t committed to running. I didn’t know whether I would run or not."

Why Clinton's explanation doesn't add up

There are a few problems with Clinton's explanation.

For one, the year in question is 2013. Yes, Clinton had stepped down from her government position as secretary of state. But she said at the time she was already openly considering running for the White House. And even if she hadn't been, it's hard to imagine neither she nor the banks expected her to again be in a position of power.

"Politicians often leverage their political talent and celebrity for personal financial gain, and paid speeches are common after they leave office," said Josh Stewart, deputy communications director for the Sunlight Foundation. "What is unique is a potential presidential candidate choosing to accept top dollar from one of the nation's largest investment banks."

Then there's the question of how much she was paid. In the above exchange, Clinton suggests that she didn't have a role in ensuring that she received a certain amount from Goldman. But as Gawker's Ashley Feinberg points out, Clinton's minimum speaking fee was $200,000.

In some ways, Cooper's question actually undersells the amount of money Clinton received. Including the $675,000 from Goldman, Clinton pulled in $2.3 million from speaking to a handful of firms in 2013, including Deutsche Bank, Morgan Stanley, Fidelity Investments, and Bank of America, according to the Intercept.

Why do those firms give so much money to potentially powerful figures?

By saying that she doesn't know why Goldman Sachs paid her $675,000, Clinton is exposing herself to one attack line while shielding herself from another.

Her enemies have long alleged that she's coy about revealing her true motivations. Saying she has no idea why she received this money plays into this critique, and contributed to the round of negative headlines that followed her remarks Wednesday night.

But in another way, Clinton's deflection here makes sense. Pleading ignorance simply doesn't sound as bad as openly acknowledging what campaign finance experts say is the truth: Wall Street firms pay high speaking fees in order to have influence with policymakers in government.

"You have one part of the economy with a lot of capital and another part that has a role determining policy," says Bob Biersack, senior fellow at the Center for Responsive Politics. "This is reflective of the way these two parts of the world interact with each other and reinforce each other."

This influence is sometimes hard to pin down. It doesn't entail a strict quid pro quo, but rather makes it more likely that Clinton will turn to someone from Goldman for advice when formulating policy related to investment banking, and more likely that Goldman will be able to reach out to her, according to campaign finance experts.

In the long term, Biersack said, that could pay big dividends for the investment bank.

"It's human nature that you're going to look for information from those who you've dealt with and who you know, and who you know understand the subject matter," Biersack says. "That can be a very small group."

There's another possible benefit to Goldman: having Clinton understand its perspective on policy.

"(Clinton) starts with a short speech, and then there's a conversation — and that has benefits for Goldman way beyond having an important person on the dais," Biersack said.

In other words, Goldman may be paying for Clinton to listen as much as it's paying her to speak.

"The bankers think: 'I need to understand her, to know where she's coming from — and for her to spend face time with me and be aware of our concerns, of the concerns as Goldman as an institution,'" Biersack said. "What better way to do that than to get her in the room?"

The irony of criticizing Clinton's ties to Wall Street: She may have the most comprehensive regulatory proposals

There's some irony to Clinton facing criticism for being too close to the financial industry, given the aggressive plans she's outlined to break up the biggest banks, implement a "financial transactions tax," and regulate the shadow banking sector.

"She has the most detailed, and arguably the strongest, financial regulation plan of the three Democratic candidates," wrote Vox's Ezra Klein in November 2015.

On Wednesday night, Clinton again defended her plans as both more effective and more comprehensive than those of Bernie Sanders.

"Anybody who knows me, who thinks they can influence me, name anything they’ve influenced me on. Just name one thing," Clinton said. "I’m out here every day saying I’m going to shut them down. I’m going after them."

But the Goldman speaking fees remain, at least politically, a problem for Clinton's candidacy.

"It's the kind of behavior voters should take into account when considering whether they want to give a candidate the unparalleled power of the presidency," wrote Vox's Jonathan Allen in May 2015. "It goes to the most important, hardest-to-predict characteristic in a president: judgment."

And there's reason to believe Clinton recognizes the liability. On Wednesday, Politico reported that Clinton postponed a fundraiser scheduled to be held by Jonathan Lavine, managing director of Bain Capital affiliate Sankaty Advisors. It was the second financial services fundraiser she'd canceled in two weeks.

VIDEO: Hillary Clinton's speech from the Iowa Caucuses