Bernie Sanders draws contrast with Elizabeth Warren: She says 'she is a capitalist through her bones. I'm not.'

With Sen. Elizabeth Warren continuing to climb in Democratic presidential primary polls, in part, at the expense of his own campaign, Sen. Bernie Sanders explicitly highlighted a key difference in their core economic philosophies in an interview with ABC's "This Week."

"There are differences between Elizabeth and myself," Sanders, I-Vt., said in an interview with ABC News Chief White House Correspondent Jonathan Karl. "Elizabeth, I think, as you know, has said that she is a capitalist through her bones. I'm not."

The statement comes as Sanders, whose Democratic Socialist ideologies positioned him as Hillary Clinton's chief progressive rival in 2016, has found himself overtaken by Warren in the majority of national and early state surveys in recent weeks, leading to questions -- particularly in the aftermath of the heart attack he suffered last week -- about the viability of his 2020 campaign in a very crowded field.

In 2018, Warren was quoted as saying "I am a capitalist to my bones" during an event hosted by the New England Council, a non-partisan regional business organization.

Sanders pushed back at the idea that he and Warren hold "identical positions," and added, of the notion that voters would prefer the similarly liberal Warren given she is younger and free of health concerns, that he is the sole candidate willing to take on the nation's "ruling class."

"I am, I believe, the only candidate who's going to say to the ruling class of this country, the corporate elite: Enough, enough with your greed and with your corruption," Sanders said. "We need real change in this country."

Sanders noted that he and Warren have been friends "for some 25 years," and he thinks "she is a very, very good senator," but again contrasted their different economic beliefs.

"Elizabeth considers herself -- if I got the quote correctly -- to be a capitalist to her bones," he said. "I don't. And the reason I am not is because I will not tolerate for one second the kind of greed and corruption and income and wealth inequality and so much suffering that is going on in this country today, which is unnecessary."

Feeling 'very well'

The senator's heart attack less than two weeks ago arrived at an inflection point for a campaign facing sliding poll numbers while simultaneously posting the single-largest fundraising quarter of any Democratic candidate this year -- a reported $25.3 million from July through September.

Sanders was hospitalized for three days and had two stents inserted to relieve a blocked artery. But he said on Saturday, and throughout the past week, he feels "very well" and that his doctors are on board with an eventual return to the "vigorous" campaign schedule that saw him regularly make three to four stops per day.

"'Heart attack' is a scary word," he told Karl on "This Week" Sunday. "What I had is a 45 to 50 minute procedure, two stents were placed in my heart, which had a blocked artery. This is a procedure, as I understand it, done many, many hundreds of thousands of times a year. It's a fairly common procedure, and people are back on their feet pretty soon, as is the case with me."

As for releasing his medical records, Sanders again promised he would do so "as soon as we can" and "with all of the information that's available," a standard he said should "should be applicable to all candidates."

"I think when you're running for president of the United States," he added, "the American people have a right to know the condition of your health."

'Will Mitch McConnell do the right thing?'

Though much of Sanders' attention is focused on the presidential race, he indicated his approval of the ongoing House of Representatives impeachment inquiry into President Donald Trump's actions with regard to Ukraine, voicing that he hopes it moves "forward as expeditiously as it possibly can."

"I think at the end of the day, the evidence is there to impeach Trump. Now, here is the real issue that we should be talking about, and that is, what happens if, and as I expect will be the case, Trump is impeached in the House?" Sanders asked. "Will Mitch McConnell do the right thing? Will he have a full trial where the American people as senators -- I'll be one of them -- can hear the evidence regarding what Trump did?"

"I am nervous that McConnell will put party in front of country and not do that," the senator continued.

'The difference between Trump and me is he lies

Sanders also was critical of Trump's decision to withdraw U.S. troops from Syria, opening the way for maneuvers by Turkish troops -- a move met with bipartisan backlash in Washington. Though Sanders has previously decried "endless wars" resulting from American military intervention abroad, he worried that the action would send a negative message to U.S. allies.

"What does it say to the entire world that you have a president who gets off the phone with [President Recep Tayyip] Erdogan of Turkey and then sends out a tweet that says, 'Oh, by the way, we're deserting [Syrian Kurds] who have put their lives on the line to work with us in fighting against some of the worst terrorists in the world," Sanders said on "This Week."

But when asked by Karl whether Trump's rationale for pulling the military out of the Syria -- at one point this week saying that the U.S. is "not a police force" -- "sounded a little bit like Bernie Sanders," the Vermont senator was quick to refute the point.

"But the difference between Trump and me is he lies," Sanders said. "I don't."