(AP) -- Hillary Clinton gave a spirited defense Thursday of her campaign proposals and her lead in the Democratic primaries after she was disrupted by a group of Bernie Sanders supporters ahead of her home state's primary.

A few minutes into Clinton's remarks on the campus of Purchase College, about 20 Sanders supporters shouted, "If she wins, we lose," and then began walking out. Clinton responded sharply, "The Bernie people came to say that. We're very sorry you're leaving," as the crowd chanted, "I'm with her!"

At another point, Clinton grew angry when Eva Resnick-Day, an organizer with Greenpeace USA, asked whether she'd forego contributions from the fossil fuel industry.

"I have money from people who work for fossil fuel companies," Clinton said in a video posted and later confirmed by Greenpeace.

"I am so sick of the Sanders campaign lying about that," Clinton added, pointing her finger at the questioner. "I'm sick of it."

The sharp exchanges came ahead of Tuesday's Wisconsin primary and next month's vote in New York, where Clinton is favored because of her deep ties to the state. The former New York senator holds a formidable lead among delegates but Sanders hopes a series of recent victories out West might turn into a springboard for a win in Wisconsin.

It also offered a vivid example of Clinton's gulf with some young Democrats, who have brought energy to the Vermont senator's upstart bid.

Clinton said she regretted that the young Sanders supporters "won't listen to anybody else" and didn't want to hear "the contrast between my experience, my plans, my vision, what I know I can get done and what my opponent is promising."

Sanders "goes around telling young people that he's going to give them free college. Well, I wish it were so," Clinton said. She said the "fine print" of his plan would require governors to pay a significant share of the cost, an unlikely outcome in a state like Wisconsin, which is led by Republican Gov. Scott Walker.

"I just wish that there were an opportunity to actually talk and listen to each other because we've got to unite when this primary contest is over," Clinton said. "We've got to unite and make sure we have a Democrat in the White House."

Sanders campaigned in Pittsburgh, ahead of Pennsylvania's April 26 primary, joining activists with the United Steelworkers union and the letter carrier's union to criticize Clinton's past support of certain trade deals.

He called for "a moral economy, not an economy based on greed and selfishness," a message that he has used in manufacturing states such as Michigan and Wisconsin. Sanders said that even when factories don't close, the trade agreements relegate workers in a "race to the bottom," with corporations going to unions and forcing them to make concessions under threat of moving out of the country.

Sanders campaign said he had raised more than $40 million in March and was aiming to surpass $43.5 million for the month. Both campaigns face monthly fundraising deadlines at the end of the day.

In New York, Clinton reiterated her critique of Sanders' "Medicare for all" plan, saying it would force Congress to "start all over again" on health care reform. She also rebuked Republican Donald Trump for saying that women should be "punished" for having an abortion, comments he quickly backtracked from.

Clinton also noted an MSNBC interview in which Sanders suggested Trump's comments were a distraction from serious issues. "To me this is a very serious issue and it is a very serious discussion," Clinton said.

Clinton's event held some nostalgia for the former first lady and secretary of state, who formally launched her Senate campaign on the campus in February 2000 and lives in nearby Chappaqua. She was introduced by Rep. Nita Lowey of New York, who noted that Clinton was her "constituent."

Meanwhile, Sanders missed the filing deadline to get on the ballot for the final primary of 2016 -- in the District of Columbia -- but local Democratic Party leaders insist it was their mistake, not that of the Sanders campaign.

Candidates can get on the ballot in the nation's capital by submitting petitions or by paying a $2,500 fee to the local Democratic Party. Hillary Clinton's campaign did both. The Sanders campaign paid the fee.

D.C. Democratic Party Chairman Anita Bonds said there's time to correct the mix-up and that Sanders' name will appear on the ballot for the June 14 primary.

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Associated Press writer Joe Mandak in Pittsburgh and Ben Nuckols in Washington contributed to this report.