Thundering against a Republican Party he accused of living in a “parallel universe,” Sen. Bernie Sanders of Vermont brought his populist roadshow to his hometown of New York City today, firing up thousands at a fundraiser and rally.

Mr. Sanders, an independent gaining ground on Hillary Clinton in the Democratic primary for president, railed against Republican candidates who he claimed were ignoring progressive issues fundamental to Americans. In his trademark grumble, Mr. Sanders, a self-identified socialist, attacked the crowded GOP field, which locked horns during a marathon televised debate on Wednesday.

“Some of you may have had the misfortune as I did the other night of watching the Republican debate,” Mr. Sanders said at Town Hall, a historic concert hall in Midtown. “The energy was just leaving my body.”

Though Mr. Sanders’ advisers had said he would swear off negative campaigning, a large chunk of his remarks were dedicated to lacerating Republicans, who he said won elections by dividing “white from black, straight from gay, men from women, people born in this country form people who are not born in this country.”

“In their three hour discussion, some of the most important issues facing the American people were not discussed at all. It is like a parallel universe,” Mr. Sanders said. “I can’t understand how in a three hour debate there was virtually no discussion of the grotesque level of income and wealth inequality in America today.”

Though Mr. Sanders delivered a typical version of his leftist fire-and-brimstone address, his performance has evolved since he first traveled the country earlier in the summer. Introduced by actor Mark Ruffalo and Jerome Thompson, a technician and union member fired by Cablevision for calling the company a “plantation,” Mr. Sanders quickly spoke about the need for criminal justice and immigration reform, critical issues for the nonwhite voters who may decide the primary. Mr. Thompson, an activist in the Black Lives Matter movement, said Mr. Sanders would fight to end “institutional racism.”

A Brooklyn native, Mr. Sanders has eschewed much of the pageantry of political campaigns, including cracking jokes and getting personal. But Mr. Sanders brought his wife, son and grandchildren to the stage, where sign-waving supporters sat and cheered. Mr. Sanders even peppered a few laugh lines in his 45 minute speech.

On the GOP’s propensity to assail President Barack Obama, Mr. Sanders quipped that they even blamed the weather on him: “Too cold, too hot, it’s raining? It’s Obama.”

On Donald Trump, the billionaire improbably leading all Republicans in the polls, Mr. Sanders was plenty sarcastic: “I did hear some brilliant discussion [during the GOP televised debate] on social security, I did. And Donald Trump is worth billions has volunteered not to take his social which will clearly address the social security issue.”

Even the fact that he was holding a fundraiser was some evidence of a maturing Candidate Sanders. Unlike Ms. Clinton and most candidates in the race, Mr. Sanders has avoided fundraising events, choosing instead to draw from a deep well of online donors. “These are the kind of fundraisers we do,” he said to cheers. “We don’t have a small room of people who contribute a million dollars a piece.”

Mr. Sanders said the Republicans peddle a “fringe agenda” beholden to a millionaire and billionaire class out of sync with most Americans.

“In my view, the Republican Party has an agenda that’s maybe a fringe agenda representing maybe 5, 10, 15 percent of the American people,” he said. “You go out to any community in America. You go out to the most conservative states in America. You say to people, ‘Hey, you think it’s a good idea that we give tax breaks to billionaires … and at the same time cut social security, Medicare, Medicaid, environmental protection.'”

“And what Americans across the board will say to you, will look you in the eye and say to you, ‘Are you nuts?'” he added.

Mr. Sanders targeted the media, including the Wall Street Journal, for questioning the price tag of his many campaign proposals, including a massive medicaid expansion and free public colleges for all. The newspaper is owned by Rupert Murdoch, a conservative billionaire.

“Now I’ve been criticized by the Wall Street Journal. Can you believe it? Rupert Murdoch and his friends just don’t like some of my ideas,” he said with a smile.