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WASHINGTON — Hillary Clinton slammed Donald Trump on Thursday for again declining to answer a question about where President Barack Obama was born, asking: "When will he stop this ugliness, this bigotry?"

"He's tried to reset himself and his campaign many times. This is the best he can do. This is who he is so we need to decide who we are," Clinton said at The Congressional Hispanic Caucus Institute awards gala in Washington, D.C.

Trump late Wednesday in an interview with the Washington Post declined to say if he believes Obama was born in Hawaii. "I'll answer that question at the right time," Trump said. "I just don't want to answer it yet." The interview was published Thursday.

Related: Trump Again Refuses to Say Obama Was Born in U.S.

Trump's campaign countered late Thursday that the candidate does believe Obama was born in the U.S., despite Trump's continued refusal to explicitly say so himself when questioned over the last year.

"Having successfully obtained President Obama’s birth certificate when others could not, Mr. Trump believes that President Obama was born in the United States," Trump campaign spokesman Jason Miller said in a statement Thursday night.

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Clinton's campaign was not convinced. Campaign spokesman Brian Fallon said "Trump needs to say it himself."

Trump needs to say it himself. On camera. And admit he was wrong for trying to delegitimize the country's first African American President — Brian Fallon (@brianefallon) September 16, 2016

Trump famously questioned Obama’s birthplace, leading Obama to release his birth certificate in 2011.

Clinton seized on Trump's non-answer during a speech at the awards gala shortly before the Trump campaign spokesman's statement.

"If we just sigh and shake our heads and accept this, then what does that tell our kids about who we are?” Clinton said. "We need to stand up and repudiate divisive rhetoric. We need to stop him conclusively in November in an election that sends a message that even he can hear."

Trump has on several occasions over the last year declined to comment on his prior questions about Obama's birthplace.

Trump in September of 2015 told "Late Show" host Stephen Colbert said "I don't talk about it anymore" in response to a question about Obama's birthplace, and the GOP nominee gave a similar answer to MSNBC's Chris Matthews in December.

But in the last week Trump campaign manager Kellyanne Conway and adviser Rudy Giuliani said that Trump now believes Obama was born in the U.S. Trump did not dispute Conway's statement during his interview with the Washington Post.

The gala speech marked Clinton’s second event back on the trail after a bout with pneumonia that sidelined her for three days.

Obama spoke before Clinton’s speech Thursday. He criticized Trump for his proposed "wall" on the U.S.-Mexico border, and said immigration reform can't be tackled by one leader.

"It's gonna take all of us. This is not something that a president can do alone. It's not something the next president will be able to do alone either, no matter how tough she is," Obama said, making an obvious reference to his preferred successor.

Related: Donald Trump Accepts Barack Obama Born in U.S., Giuliani Says

In her opening remarks, Clinton made a pointed joked about a Latino Trump surrogate who warned that taco trucks would be "on every corner" if Trump isn't elected president.

"I personally think a taco truck on every corner sounds absolutely delicious,” she said to laughs in the convention center hall.

The former secretary of state also reiterated her commitment to introducing comprehensive immigration reform in her first 100 days in office, if elected.

"Fighting for kids and families. That’s been the cause of my life. It will be the passion of my presidency," she said.