BRASILIA — On Sunday, a historic vote in the Brazilian Congress will decide whether President Dilma Rousseff is to face an impeachment trial.

In the meantime, though, many Brazilians are worried that her vice president, Michel Temer, who will take over if she is ousted, has already decided that her job is his.

Their concern was provoked this week when Temer sent some lawmakers on a WhatsApp group a speech in which he spoke as if the vote had taken place and Rousseff had lost. In the nearly 14-minute audio text, he promised a government of “national salvation" and declared, “Without this national unity, it will be difficult to get this country out of the crisis we find ourselves in.”

Temer claimed he had meant to send the speech only to a friend but accidentally sent it to the wider group. Few believed him.

In addition, his Wikipedia page was altered to describe him as “a Brazilian lawyer and politician currently serving as the 37th president of Brazil since April 2016,” adding, “He took office after the former president Dilma Rousseff was impeached during her second term.”

The page has since been amended — but not before the original changes were widely circulated on social media. The question now is whether the scent of power has caused Temer — a discreet, smartly suited lawyer who in a leaked letter to Rousseff last year complained his role was largely decorative — to lose his usual composure.

Temer’s presidential ambitions drew fire from Rousseff’s predecessor and political mentor, Luiz Inácio Lula da Silva, in a speech this month. “Temer, you want to be president? Then fight an election, my son,” Lula cackled.

Like the Workers' Party to which Rousseff and Lula belong, Temer’s Brazilian Democratic Movement Party, or PMDB, has also been implicated in a multibillion-dollar bribery and kickbacks scandal at the state-run oil company Petrobras. The scandal is a key factor in the push to oust Rousseff and her government.

Temer was named in testimony provided by a former government senator who alleged that the vice president was involved in an illegal ethanol-buying scheme and had been behind the appointment of an executive to a top Petrobras job. The executive, Jorge Zelada, was sentenced to 12 years in prison for his part in the scandal by a lower court. Investigators say that parties like the PMDB and the Workers’ Party chose key Petrobras department chiefs and were able to skim bribe money off contracts as a result. Temer denies the allegations, as do the PMDB and the Workers' Party.

Separately this month, a request was delivered to the lower house to also impeach Temer. The request is stalled in the Supreme Court but has already had an  impact on public opinion. In a recent poll in which 61 percent of the respondents said they supported Rousseff’s ouster, 58 percent also said they supported Temer’s impeachment.

The PMDB is Brazil’s biggest party and has been around for 50 years. Its members have served in all but one of Brazil’s governments since the country returned to democracy in 1985 after two decades of military dictatorship. Until recently, Temer was its president.

The youngest of eight, he was born in 1940 into a family of Lebanese immigrants in Tiete, in the interior of Sao Paulo state. He studied law at the prestigious University of Sao Paulo, received his doctorate at the city’s Pontifical Catholic University, served as the Sao Paulo state attorney general and in 1986 entered Congress as a federal deputy for the PMDB.

Until the current crisis began to unfold, Temer was an unobtrusive figure in Brazilian politics, known for his sleek suits and slicked-back hair. When Rousseff won her first mandate in 2010 with Temer as her vice president, both he and the unmarried president were upstaged at the inauguration ceremony by Temer's wife, Marcela, a former model 43 years his junior.

Temer’s image problem is compounded by Eduardo Cunha, his party’s confrontational speaker of the house, who himself faces charges in the Supreme Court over the Petrobras scandal. Brazilians worry that if Temer does become president, he may seek to sanitize the charges against both him and Cunha.

For an impeachment trial to proceed against Rousseff, two-thirds of the members of the lower house must vote in favor. If they do, and if the Senate approves that vote, Temer takes over as interim president, and it is widely considered unlikely that Rousseff will be able to resume office.

As an unpopular president for whom nobody ever voted, it will be a challenge for Temer to convince Brazilians he can do the job. But his leaked speech did succeed in getting one potentially effective message out.

He said that a government under him would preserve government social policies including a cash transfer scheme to low-income Brazilians called the Bolsa Família, or Family Allowance. The PMDB has promised austerity measures to fight Brazil’s recession. But messing with the Bolsa Família, which one in four Brazilians receive, could be politically disastrous.

The speech backfired in another direction, however. In an interview with the Globonews TV channel, Temer said he had accidentally sent it to a WhatsApp group of politicians rather than to an old friend, as he intended, because he was unused to handling his cellphone. Normally, he said, an aide did that for him.

The idea that the potential new president of Brazil does not know how to use the popular messaging service, let alone his cellphone, probably did little to win the confidence of the scores of millions of Brazilians who manage those simple tasks every day.