Hillary Rodham Clinton was ready when CNN's Anderson Cooper questioned at the start of Tuesday night's presidential debate the many changes in positions she has had since she began running for president.

"Will you say anything to get elected?" he asked. She responded this way:

Well, actually, I have been very consistent. Over the course of my entire life, I have always fought for the same values and principles, but, like most human beings — including those of us who run for office — I do absorb new information. I do look at what's happening in the world.

That's absolutely the right answer for a politician to give. I've been guided by consistent values and principles but I am also open to new information and, when presented with it, I reassess certain positions on certain issues. I've always wondered why more politicians don't give that answer when confronted with obvious changes in their positions rather than insist they have had the same views on every issue forever. Everyone has evolved in some, way, shape or form on an issue in light of new information and, if someone hadn't, would we really want to elect a person like that president?

That said, I'm not sure Clinton's explanation for her flip-flops will convince her doubters (or even some of her allies). Here's why.

1) In each of her "evolutions" on issues, Clinton has moved from a less popular position within the Democratic base to a more popular one. She went from opposing same-sex marriage to supporting it. (President Obama made the same move.) She went from calling the Trans-Pacific Partnership the "gold standard" of trade deals in 2012 to opposing it in 2015. In each case, Clinton's decision to change positions seemed to have an obvious political motivation — to shore up her liberal flank as she faces a more serious-than-expected challenge from Sen. Bernie Sanders (I-Vt.).

Could it be a coincidence that the new information Clinton has acquired in each of these cases led her to take the position shared by the liberal wing of her party? Sure. But as the old saying goes, there are no coincidences in politics.

2) The key to Clinton selling her policy switches hinges on the idea that she is absorbing new information that forces a reevaluation. But it's not entirely clear what exactly the "new" information would be on, say, same-sex marriage — other than polling that showed the public growing more and more comfortable with the idea. And, on her TPP flip-flop, here's how Clinton explained the "new information" that changed her mind:

I did say, when I was secretary of state, three years ago, that I hoped it would be the gold standard. It was just finally negotiated last week, and in looking at it, it didn't meet my standards. My standards for more new, good jobs for Americans, for raising wages for Americans.

Hmm. What exactly was the new information she acquired and how did it not meet her "standards"? We don't know — and her standards for "more new, good jobs for Americans" are, it goes without saying, totally subjective and amorphous. Remember, too, that when Clinton referred to TPP as the "gold standard" in 2012 -- she never said she "hoped" it would be; she said it was -- and she insisted that it would "open free, transparent, fair trade, the kind of environment that has the rule of law and a level playing field. And when negotiated, this agreement will cover 40 percent of the world's total trade and build in strong protections for workers and the environment."

What changed her view? Why? How? When? We don't know — and in the absence of that knowledge, it sure looks like political expedience.

3. Clinton is battling the broader perception that she is not honest and trustworthy, which makes it hard to sell her changes in position as genuine evolutions based on study and reflection rather than calculated moves to get her right with the base in the face of the Sanders's surge. It's never easy to sell a position change in politics — because of the unreasonable expectation we have that our politicians be consistent in everything always — but it's especially hard when a storyline already exists that you are, at root, a politician who lacks a set of core convictions. Mitt Romney learned that lesson in 2008 (and 2012) as he abandoned past positions on abortion and health care, moving to the right in hopes of convincing the GOP base that he was one of them. (It didn't work.)

Sometimes politicians can give the exact right answer to a tough question and still not solve their problems. That seems likely to be the case for Clinton, who may be too bogged down in her past public perception and the seeming political advantage she gains from these position shifts to convince people that her switches are principled evolutions.