Bernie Sanders on Friday doubled down on criticism of fellow Democratic presidential candidates Pete Buttigieg and Joe Biden over the support they’ve received from billionaire donors, arguing his 2020 rivals’ fundraising was “exactly the problem with American politics”.

Sanders noted that the South Bend mayor, Buttigieg, had accepted support from 40 billionaires throughout his campaign and was “closing in on Biden”, the former vice-president who has received donations from at least 44 billionaires. The Vermont senator told the Guardian: “They will tell you, ‘It doesn’t impact me. It really doesn’t mean anything to me.’ That is clearly nonsensical. Why would billionaires and wealthy people be making large contributions if it didn’t mean something to them?”

Sanders appeared cheerful and spoke confidently about the state of his presidential campaign as he sat down with the Guardian and the not-for-profit publication Capital & Main before a climate town hall in Moreno Valley, just outside of Los Angeles. He discussed his odds in the early primary states and his policy priorities in the White House, one day after the final Democratic debate of the year.

On Thursday, Sanders had faced off with six opponents in an at times heated debate, which was marked by escalating attacks on Buttigieg, the 37-year-old centrist mayor who has been rising in the polls in early primary states.

Buttigieg faced questions over his lack of experience in national politics and repeated criticism for a lavish fundraiser in a California “wine cave”. The mayor countered he was willing to accept money from anyone who wanted to defeat Donald Trump.

That attitude has created “candidates who are not addressing the needs of working class people, but are working overtime to protect the wealthy and the powerful”, Sanders argued on Friday, rattling off statistics on the extreme expansion of income inequality over the last 30 years in the US. “The agenda of the wealthy … is implemented by their campaign contributions and their access to candidates.”

Sanders also brushed aside concerns from some Democratic pundits, who have drawn comparisons between him and Jeremy Corbyn, the British Labour leader who experienced a stunning defeat in that country’s recent elections. “Our opponents will throw every reason in the world against us,” Sanders said, arguing his rise is making the Democratic establishment “very, very nervous”.

Why would billionaires and wealthy people be making large contributions if it didn’t mean something to them? Bernie Sanders

He continued, “The United Kingdom, last I heard, is not the United States. Brexit is not a major part of what this campaign is about. The issues that I am campaigning on, in fact, are precisely the issues the American people support. Talk about raising the minimum wage to 15 bucks an hour. Four years ago when I introduced that concept, it was a radical idea. Not radical anymore.”

Sanders noted that there was also polling showing broad support for many of his more progressive proposals, including Medicare for All, student debt cancellation and wealth taxes.

In his first weeks in office, Sanders said, he’d pursue a wealth tax, infrastructure legislation to spur new job growth, his signature Green New Deal climate plan, efforts to make it easier for workers to unionize and a push to close the wage gap for women. He’d also work on an executive order to ensure that contractors with the federal government pay workers a minimum of $15 an hour.

“We have the message to appeal to working people. We are investing in this campaign very heavily in a grassroots effort here in California. It’s unprecedented, I think it is fair to say.”

The Sanders campaign has invested heavily in organizing in California, recognizing the growing importance of the state in the primary race. Roughly 14 million voters will be eligible to participate in the state’s 3 March Democratic primary. Sanders has held rallies in cities across the state, and has built a large grassroots infrastructure to spread his message.

California polls have shown him performing well among Latino voters, a bloc that will be critical as the race heats up. Sanders and Warren have been near the top in recent polls across the country, though the progressive senators have largely continued to trail Biden, considered the most moderate frontrunner.

Among the toughest questions Sanders faced during the debate were several on race and identity. When asked about concerns regarding too many older men in power, he interjected, “And I’m white as well!” adding, “The issue is not old or young, male or female, the issue is working people standing up taking on the billionaire class.” When he pivoted to the climate crisis on a question about racism, he earned a rebuke from a moderator.

Asked about the nearly all white lineup at Thursday’s debate, the senator promised on Friday, “When people turn on the television and see my cabinet and our administration, it will look like America … in terms of racial diversity, ethnic diversity, religious diversity … We’ve got to work hard to undo the racism and the xenophobia of the Trump administration and one way you do that is to create an inclusive administration.”

He declined to say whether he would select a vice-president running mate who was a person of color: “It’s too early.”

Asked if he had fun at the debate, the senator sighed. “Fun is the wrong word. It’s frustrating! You don’t have time to get into the issues.”