BRASÍLIA — In a stunning twist in the effort to impeach President Dilma Rousseff of Brazil, the new speaker of the lower house of Congress has changed his mind — less than 24 hours after announcing that he would try to annul his chamber’s decision to impeach her.

Brazilians awoke on Tuesday to the news of the sudden about-face by the speaker, Waldir Maranhão, who on Monday was widely ridiculed and threatened with expulsion from his Progressive Party for trying to upend the impeachment process.

Mr. Maranhão said on Monday that he would to try to annul the April 17 impeachment vote against the president, citing concerns about procedural irregularities. But in a decision made around midnight here, and widely circulated in the early morning on Tuesday, Mr. Maranhão told Renan Calheiros, the head of the Senate, that he was revoking his earlier decision.

The head-spinning change of course was only the latest development in a political crisis that has mesmerized and bewildered Latin America’s most populous nation.