Brazil's senators are debating whether to put President Dilma Rousseff on trial over allegations that she illegally manipulated the budget to hide a growing fiscal deficit.
Wednesday's debate will be followed by a vote that could suspend Rousseff, the first woman to become Brazilian president, for the duration of the investigation, which will be 180 days.
A two-thirds majority in the upper house is what is required to remove her from office permanently.
Al Jazeera's Latin America Editor Lucia Newman, reporting from Brasilia, said Rousseff was expected to lose by an overwhelming majority.
"It is a dramatic time for Brazil," she said. "Even the pope has weighed in, calling for prayers and dialogue."
In a possible sign that she was preparing for a defeat, Rousseff was expected to dismiss all her ministers late on Wednesday to give Temer a clean slate to name his own cabinet, according to Humberto Costa, a ruling Workers' Party senator.
Earlier on Wednesday, Brazil's Supreme Court rejected an appeal to block the Senate vote.
In April, the lower house of parliament voted to impeach Rousseff, who has been president since 2011.
But on Monday, Waldir Maranhao, the interim head of the legislature's lower house, threw the impeachment effort into disarray by annulling that vote, citing procedural problems.
He then reversed the decision several hours later, setting the stage for the vote in the Senate.
Deeply unpopular, Rousseff's presidency has been damaged by corruption scandals, political paralysis and a sharp economic downturn.
About 11 million people are out of work.
Rousseff faces impeachment over accusations of tampering with figures to disguise the size of Brazil's budget deficit during her 2014 re-election campaign.
She has denied any wrongdoing, and cast the efforts to remove her as a coup.
Source: Al Jazeera and agencies