NEW YORK >> President Barack Obama on Monday defended his view that gay couples should have the right to marry, saying that the country has never gone wrong when it "expanded rights and responsibilities to everybody."

"That doesn’t weaken families. That strengthens families," he told gay and lesbian supporters and others at a fundraiser hosted by singer Ricky Martin and the LGBT Leadership Council. "It’s the right thing to do."

The remarks were his first to such an audience since he announced his personal support for same-sex marriage last week. They came on a day that Obama was making a targeted appeal to three core voting blocs — women, young people, and gays and lesbians. He gave a commencement address to Barnard College, a women’s college, and taped an interview on "The View," a popular day-time talk show aimed at women.

Democrats hope Obama’s politically risky embrace of gay marriage will re-energize supporters who had been frustrated by his previous assertions that his views on the hot-button social issue were "evolving."

Women, young people and gay voters all made up crucial voting blocs for Obama in the 2008 election. With the president locked in a close race with Republican rival Mitt Romney, his campaign is focused on rallying support among those groups once again.

"At root, so much of this has to do with a belief that not only are we all in this together but all of us are equal in terms of dignity and in terms of respect, and everybody deserves a shot," he told about 200 supporters at the fundraising event.

Obama also called for repealing the Defense of Marriage Act, a federal law that defines marriage as being between a man and a woman. His administration has refused to defend the law in court challenges, and while Obama has voiced support for its repeal before, he specifically listed repeal as a goal.

Romney has said he believes that marriage is defined as being between a man and a woman. Although Obama did not mention Romney’s stance, he cast his challenger as a "rubber stamp" for congressional Republicans and cited his 2008 opponent, Sen. John McCain, as a far more independent Republican who believed in climate change and in the need for overhauling the immigration system.

"What we’ve got this time out is a candidate who’s said he would basically rubber stamp the Republican Congress and who wants us to go backwards and not forward," Obama said.

Earlier in the day, during his address at Barnard, Obama urged the graduates to fight for their place at "the head of the table" and help lead a country still battered by economic woes toward brighter days. "I believe that the women of this generation will help lead the way," he said.

The president’s choice of Barnard as his first commencement address of the spring underscored the intense focus both candidates have placed on women. An Associated Press-GfK poll conducted earlier this month showed Obama with a sizable advantage over Romney with women voters, 54 percent to 39 percent.

Obama acknowledged that today’s college graduates are entering a shaky job market. To those who say overcoming the nation’s challenges isn’t possible, Obama said, "Don’t believe it." He told the graduates that if they ever despair, they should think of the country’s history and what young generations before them have achieved.

"Young folks who marched and mobilized and stood up and sat in from Seneca Falls to Selma to Stonewall they didn’t just do it for themselves, they did it for other people," Obama said. "That’s how we achieved women’s rights, that’s how we achieved voting rights, that’s how we achieved workers’ rights, that’s how we achieved gay rights, that’s how we’ve made this union more perfect."

After the speech, Obama taped an appearance on ABC’s "The View," which was to air Tuesday. When asked if he would personally fight to repeal the Defense of Marriage Act, he replied, "Well, look, Congress is clearly on notice that I think it’s a bad idea." He also pointed to the $2 billion loss in high-risk trading at JPMorgan Chase to reiterate the need for Wall Street reforms.

Tickets for the fundraiser hosted by Martin and the LGBT Leadership Council started at $5,000 per person.

A new poll by the Pew Research Center found that about half of those surveyed say Obama’s support for same-sex marriage does not affect their opinion of the president, with about one-fourth saying they feel less favorably toward him and 19 percent feeling more favorably.

There was a big disparity between older and younger adults surveyed, indicating a more intensely negative reaction among older Americans. Forty-two percent of people over the age of 65 said they viewed the president less favorably because of his decision, while 62 percent of respondents between the ages of 18 and 29 said Obama’s announcement did not affect their opinion.