Sen. Elizabeth Warren is one of the top-tier Democratic candidates for president, near the head of the pack, along with former Vice President Joe Biden, fellow progressive Sen. Bernie Sanders and upstart Mayor Pete Buttigieg. Warren saw some of her momentum stall in national and state polls after she rolled out her proposal to pay for "Medicare for All" in early November and a subsequent plan detailing how she would transition the American health care system to a single-payer model. She also got into high-profile, public battles with billionaires such as Leon Cooperman and Lloyd Blankfein. With the Iowa caucuses coming in early February, the Democratic presidential candidates, particularly those at the top of the field, are scrambling for support among the party's rank and file. Warren on Saturday sat down with CNBC's John Harwood at the Erickson Community Center in Clinton, Iowa, to discuss the state of her campaign, her vision for remaking American capitalism and what she thinks of impeachment proceedings against President Donald Trump. An edited transcript of the interview follows. John Harwood: Do you see any lessons for yourself for Democrats, for American politics in the results of the British election the other day and what happened to Jeremy Corbyn?

Elizabeth Warren: Well, you know, I think that the Brexit part of that vote is a huge sway and it seems to me that it's clear that there was a real divide in the country, and big part of what drove that vote. John Harwood: You don't think it was a lesson that the liberal Democratic equivalent shouldn't go too far left? Elizabeth Warren: Brexit certainly wasn't the whole part. But I think that this notion of left — I don't think there's any such thing as a problem of government that works too much for the people. And that's what this ultimately should always be about. That's what all our governments should be doing. That's what a democratically elected government should do. It shouldn't just be there for the wealthy and the well-connected. It should be there to help strengthen middle class, to help give opportunities to working people. That's what government can do when it's working best. John Harwood: One issue that came up in your recent transparency battle with Mayor Pete had to do with who his clients were at McKinsey. In particular, whether or not any of the advice that he gave was used to lay off workers. He says he doesn't know; he doubts it. But if it did, is there anything wrong with that? Elizabeth Warren: So, look, I'm glad that the mayor agreed to disclose the information about his past clients, because I think the American people have a right to know in effect where conflicts are, potential conflicts of interest. But for me, this is a lot less about what was happening five years ago or 10 years ago or 15 years ago, and a lot more about what's happening every day in this primary as we go into the 2020 election season. So, it's about who are your bundlers, the people who get special access to the candidate's time, in return for agreeing to raise $25,000 or a quarter of a million dollars. Who is putting together the big parties? Who's doing the political action committees?

John Harwood: I was asking as an economic matter. You say that you're a capitalist to your bones. Elizabeth Warren: I am. John Harwood: Isn't a consultancy that advises businesses on how to be more lean and efficient part of the creative destruction that makes capitalism capitalism? Elizabeth Warren: Depends on the kind of capitalism we're talking about. I am proposing something called accountable capitalism. You may remember that, for more than a century, American corporations owed multiple duties. They owed duties to their investors, but also to their employees, to their customers, to the communities where they were located, to our country. And then, in the late '70, an economist comes along and says, "Hey, here's a novel idea. How about if you only owe any kind of duty to your investors?" Which means, make it all about profitability. That means that American corporations today, these giant corporations, they have no loyalty to America or to American workers. John Harwood: Now Jamie Dimon and the Business Roundtable came out earlier this year and said the days of sole fealty to shareholders are over; we're making some changes. Was that meaningful in your view?

Elizabeth Warren: Can we just put that in a little bit of context? I had come out with my accountable capitalism proposal that said that giant companies, like the kind of company that Jamie Dimon runs, should have to be chartered at the federal level. Their charter should actually say that they owe all of these multiple duties, and that employees can elect 40% of the board of directors to make sure. John Harwood: You think you caused them to make that decision? Elizabeth Warren: Well, all I'm saying is that's what happened first. There was a lot of conversation about it, and then Jamie Dimon and the heads of some other very large corporations said, "Oh, we don't need a law. We're just going to make that change voluntarily." John Harwood: Do you think they'll do it on their own? Elizabeth Warren: No. I think that what'll happen is, they'll say they're going to do it on their own, and they may make some adjustments. But understand this: There's a reason you put laws in place. Because the one who doesn't follow voluntarily is the one who then gets a little short-term comparative advantage, gets to boost the share price just a little bit. You put in rules so everybody competes on a level playing field. That's what we should do with accountable capitalism. If Jamie Dimon thinks it's a good idea for giant corporations like J.P. Morgan Chase to have multiple obligations, he and I agree. Then let's make that the law. John Harwood: Let me go back to the McKinsey example. Your friend Deval Patrick, the former governor, worked at Bain Capital. When he got into the race the other day, he said he thought the Obama campaign had given a bum rap to Bain when he was running against Mitt Romney. This is a part of how business works; some deals go bad, but it's not a bad thing. Do you think he's right? Is Bain Capital and what it represents in the economy a bad thing? Elizabeth Warren: When they're trying to tweak up corporate actions that are already aiming only toward increasing profitability, perfectly willing to, if they could save a nickel by moving a job to a foreign country, would do it in a heartbeat — that is a problem in our economy. Even Jamie Dimon says so. Others who come in and help them do that, that's not making our economy work any better and it's not making our country work any better.

John Harwood: Do firms like that have a constructive role to play? Elizabeth Warren: They have a constructive role to play when we have accountable capitalism. If what they were helping do is make that company work better for employees as well as shareholders, for the communities where they're located as well as shareholders, then sure. But that's not what they're doing. John Harwood: So you disagree with the governor. You don't think that Obama was giving a bad rap to Bain? Elizabeth Warren: When they're just trying to say, "the only thing that matters is the bottom line, profits, profits, profits, and whoever you have to step over to get there, and however many hardworking people you have to lay off to get there," then I think that's a problem. John Harwood: Liberal critics of the president say about his immigration policies: The cruelty is the point. He's trying to deter behavior. When you and your campaign sell mugs that say "billionaire tears," why shouldn't Jamie Dimon, Leon Cooperman, Lloyd Blankfein, Bill Gates, all the people who've complained — and ordinary voters — why shouldn't they conclude that punishment is the point? Elizabeth Warren: No, no, no. Come on. As I say in every one of my town halls, if you made it big, I mean really big, I mean top one 10th of 1% big, good for you. That's great. But pitch in 2 cents so everyone else gets a chance to make it big. Because for me, that's what this is all about. This year the (bottom) 99%, they're going to pay about 7.2% of their total wealth in taxes. The top one-tenth of 1%, those top millionaires and billionaires, fortunes above $50 million, they're going to pay less than half that, about 3.2%. And look, it's not just about asking to pay taxes, it's about what we do with those taxes. That 2 cent wealth tax would mean we could pay for universal child care for every baby in this country. That would be life-transformative for those babies who got high quality, early education experiences and get ready for kindergarten. It would be life-transformative for their mamas and their daddies who could finish school, who could move to a part-time job, who could move from a part-time job to a full-time job. The way I've set it up, it would be life-transformative for all of the child care workers and preschool teachers who would see their wages go up substantially, so they'd be paid the professional wages they deserve. And that would mean a lot of money back into the economy. It's about values. Two cents with the millionaires and billionaires, or invest that money in every one of our children and in growing our economy. John Harwood: Why do you think that those people believe that they're being vilified, believe that you hate business, believe that you're not a capitalist?

Elizabeth Warren: You'd have to ask them. But I will say this: A lot of them just don't want to pay the taxes. And that's part of the problem we've got here. Government listens disproportionately to rich guys who don't want to pay taxes. For everybody who says that this government is caught in gridlock, remember that when the question was cutting taxes for the richest and for the biggest corporations, it took the Republicans about five weeks in order to call everybody in and do a trillion and a half dollars in tax breaks, tax breaks that went mostly to those at the top. The folks at the top, they get heard all the time in Washington. I want middle-class families to get heard in Washington. John Harwood: You want to take a hammer to major structures in the American economy: break up big tech, break up big banks, ban fracking, end the private health insurance industry, $21 trillion in new taxes. I know why you want to do those things, I know your arguments for them. But are you concerned that you're going to end up breaking some things that don't need to be broken? That unintended consequences could hurt the people you're trying to help?