The lawmakers say Trump's years-long campaign challenging Obama's birthplace –– and by extension, his legitimacy to hold the office –– is rooted in racism, bigotry and the centuries-old effort by certain white voices to suppress the success of blacks.

In the harshest terms, they're accusing Trump of softening his tone in a cynical effort to attract minority voters, while calling on the GOP nominee to apologize to the president.

"Donald Trump is nothing more than a two-bit racial arsonist, who for decades has done nothing but fan the flames of bigotry and hatred," Rep. Hakeem Jeffries (D-N.Y.) said during a press briefing outside the Walter E. Washington Convention Center in Washington D.C.

Trump has long-questioned Obama's birthplace, and as recently as Wednesday he declined to acknowledge that the president was born in Hawaii.

"I'll answer that question at the right time," he told The Washington Post.

Friday, evidently, was the right time. During an event at his posh new hotel in Washington, Trump stood on stage for more than 20 minutes as veterans praised him before briefly addressing the controversy.

“President Barack Obama was born in the United States, period,” he said. “Now we all want to get back to making America strong and great again.”

"He has now been told by his advisors that he's not going to win the presidency unless he can reach out to African-American voters," Butterfield said. "His numbers are in the single digits and they will remain in the single digits."

Rep. Jim Clyburn (S.C.), the third-ranking House Democratic, said Trump's long-standing effort to question Obama's citizenship transcends the 2016 presidential race. Rather, it's part of a much broader campaign to "delegitimize" the accomplishments of the country's first black president –– and African Americans more generally.

"This man on a mission to heap as much insult on this president to do as much as he possibly can to delegitimize his presidency and to play into a narrative that has been floated in this country for over 200 years," Clyburn said.

"This is not just about the contest for the presidency."