The White House castigated MSNBC for reporting on Mr. Trump’s taxes. “You know you are desperate for ratings when you are willing to violate the law to push a story about two pages of tax returns from over a decade ago,” its statement said. “The dishonest media can continue to make this part of their agenda, while the president will focus on his, which includes tax reform that will benefit all Americans.”

The president’s son Donald Trump Jr. suggested that the disclosure only demonstrated his father’s business acumen. “Thank you Rachel Maddow for proving to your #Trump hating followers how successful @realdonaldtrump is & that he paid $40mm in taxes!” he wrote on Twitter.

Democrats pounced on Tuesday night’s report, arguing that the White House’s decision to release details of Mr. Trump’s 2005 taxes before Ms. Maddow’s show undercut his past refusal to release any such information.

“If they can release some of the information, they can release all of the information,” Zac Petkanas, a senior adviser to the Democratic National Committee, said in a statement. “The only reason not to release his returns is to hide what’s in them, such as financial connections with Russian oligarchs and the Kremlin.”

The tax forms were sent to David Cay Johnston, a former New York Times reporter who covered tax policy for years and has written a book, “The Making of Donald Trump.” Appearing with Ms. Maddow, he said he had received the forms “over the transom” at his home and did not know who had sent them. He suggested that they might even have been sent by Mr. Trump himself. Because he did not solicit the forms, Mr. Johnston said it was not illegal to receive them or publish them on his website.

The forms showed that Mr. Trump made $67 million in real estate royalties, $42 million in business income, $32 million in capital gains, $9 million in taxable interest and $998,599 in salary in 2005, for a total of nearly $153 million. After writing off $103 million, he reported adjusted gross income of nearly $49 million. In the end, he had to write a check for $2,450,597, including penalties and interest for late payment.