SALEM, N.H. – Taking aim at the newest candidate in the race for the Democratic presidential nomination, Sen. Bernie Sanders told Fox News on Monday that “I don’t think billionaires should be able to buy elections.”

Campaigning in New Hampshire, Sanders fired away at Mike Bloomberg, the former New York City mayor and multi-billionaire business and media mogul who on Sunday declared his candidacy for Democratic presidential nomination.

As the populist independent senator from Vermont was finishing up a three-day campaign swing in the state that holds the first primary in the race for the White House, Bloomberg launched TV commercials in media markets across the country that are backed up by a massive ad buy topping $30 million.

At a campaign stop in Salem, Sanders charged that Bloomberg “has decided to use all of his $55 billion, not to buy a yacht, not to buy a fancy car, but to buy the United States.”

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And in an interview with Fox News and with two New Hampshire based newspapers, Sanders pointed to Bloomberg’s strategy not to campaign in the four early voting primary and caucus states that hold contests in February and instead concentrate his firepower on the delegate-rich states that vote on Super Tuesday in early March and beyond.

He argued that Bloomberg’s “not come to New Hampshire to do the town meetings that I and other candidates have done. Not gone to Iowa, not gone to South Carolina, not gone to Nevada. What I think a campaign is about is sitting down, talking to people, hearing their experiences, letting them know you.”

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And the two-time White House hopeful emphasized “what he is doing is taking a billion dollars out of his $55 billion and saying ‘you know what, I want to buy this election.’ He is bombarding the airwaves in an unprecedented way, spending tens and millions of dollars on commercials all over this country. I don’t think that’s what American democracy is supposed to be about. I don’t think billionaires should be able to buy elections.”

But Sanders wasn’t done. He later highlighted that if he wins the nomination, it won’t be because of TV ads but rather his grassroots efforts.

“I'll tell you why I think we're going to win. It's not because of the TV ads. We have TV ads, we have radio ads. It's because we have a very strong volunteer organization that’s going to be knocking on a lot of doors and talking to a lot of people,” he noted.

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Responding to the criticism in recent days from Sanders and numerous other 2020 Democratic presidential candidates that he’s trying to buy the nomination, Bloomberg highlighted on Monday that he’s “been very successful and I’ve used all of it to give back to help America.”

“I’m committed to fight for gun safety. I’m committed to fight for stopping climate change, which is a disaster for us. I’m committed to doing things like, I was lucky enough to be able to help flip the House from Republican to Democratic control, so that the House provided some oversight of the President, which the Republican House before that had not done. I’m using my money to do things like turning Virginia from red to blue,” he noted at a stop Monday in Norfolk, Virginia -- his first campaign event since announcing his bid.

And Bloomberg said that he’s “fully committed to defeating Donald Trump. I think he’s an existential threat to our country. I’m going to make my case and let the voters, who are plenty smart, make their choice.”

Sanders was in New Hampshire soon after former Vice President Joe Biden – another of the top-tier 2020 Democratic contenders – hinted to a questioner at a town hall in Iowa that he’s considering four women to be his running mate if he wins the nomination: former Georgia gubernatorial candidate Stacey Abrams, former Assistant Attorney General Sally Yates, and Sens. Jeanne Shaheen and Maggie Hassan of New Hampshire.

Asked if like Biden, he has some potential running mates in mind, Sanders shot back that “it's a little bit presumptuous to be talking about a running mate when you haven't won the nomination yet. So there are a lot of great people out there who could be running mates, but it's a little bit too early to talk about.”

Democratic presidential candidate Sen. Bernie Sanders of Vermont takes pictures with supporters after holding a campaign event in Salem, NH on Nov. 25, 2019

Sanders crushed Hillary Clinton by 22 percentage points in the 2016 Democratic presidential primary in New Hampshire, launching the one-time long-shot into a marathon battle with the eventual nominee.

But Sanders acknowledged that it’s a very different race this time around, spotlighting that “we're taking nothing for granted.”

One way he’s been stepping things up from four years ago is taking more questions from the crowds and greeting and taking photos with those who attend his rallies.

“I think in terms of selfies, it is clear as you can see that people like that, they like the idea of coming up to candidate and doing the photographs, so we’ve been doing that on a number of occasions,” he shared.

But he refused to play a political pundit, demurring when asked where he needs to finish in New Hampshire’s primary.

Instead, he said that “no one denies that states like New Hampshire and Iowa, Nevada and South Carolina and California are enormously important. And that's why so many candidates are here in New Hampshire. So to my mind, it is terribly important that we do well, that we win this thing and we're going to work as hard as we can to do just that.”