The centre-right president was holed up at the presidential palace and was scheduled to meet later in the day with his defence minister Raul Jungmann and military commanders in an apparent show of authority despite the crisis.
But Temer, who just a few days ago was celebrating his claim to have begun lifting Brazil from a punishing recession, is now hanging on by his fingernails.
A secretly recorded conversation between Temer and a business executive purports to show the president approving payment of hush money to former lower house speaker Eduardo Cunha, who is in prison after being convicted of bribe-taking.
The allegation was first published by Brazil's powerful Globo media organisation and on Thursday, the Supreme Court opened a formal investigation.
Temer angrily insisted on national television that he will not resign. However, opponents piled on the pressure, with eight impeachment requests filed in Congress.
Late Thursday, he expressed confidence that he can keep his congressional alliance together, preventing impeachment proceedings.
"No one has come to ask me to resign. On the contrary, they're all asking me to resist. I will resist," he told Globo news site.
"I will get out of this crisis more rapidly than you think."
Take to the streets
That's not what his opponents think.
Temer's conservative government has angered millions of Brazilians with its ambitious austerity reforms, which include the planned raising of the retirement age to fix the country's unaffordable pension system.
Temer says the reforms are already helping to end a two-year recession, but with unemployment on 13.7%, many Brazilians do not feel the supposed improvements.
Temer is also loathed on the left for his role in the impeachment in 2016 of leftist president Dilma Rousseff. As her vice president, he immediately took over when she was pushed out.
On Thursday, thousands of people demonstrated against Temer in the capital Brasilia and in Rio de Janeiro. Nationwide protests were planned on Sunday, with turnout likely proving an important barometer of the national mood.
Even a former chief justice of the Supreme Court, Joaquim Barbosa, called for Temer's head.
"There is no other way out. Brazilians must mobilise, must take to the streets to forcefully demand the immediate resignation of Michel Temer," he said on Twitter.
Doing the numbers
Temer faces a perilous investigation in the Supreme Court. However, his more immediate danger is a collapse of his base in congress, opening the way to impeachment.
"That's why today the main question is to know whether the parties that form the government's base will leave," said Thomaz Pereira, a constitutional law professor at the Getulio Vargas Foundation in Rio.
So far only one minister, the culture secretary, has quit, but several others have been rumoured to have one foot out of the door. Folha newspaper referred to "a climate of confusion".
Temer's PMDB party is the biggest in congress but the key to his coalition is the centre-right PSDB Social Democrats. They have given mixed signals, but so far are staying in the government.
"Our ministers continue to work and we will not take any action with regard to their staying in the government before we have a conversation with President Temer," the party's Senate leader, Paulo Bauer, told Globo.
Ironically, the legislature that now holds Temer's fate in its hands is itself riddled with corruption scandals.
Some two-thirds of lawmakers have had brushes with the law at some point. And a third of the Senate is currently being probed in the "Operation Car Wash" investigation that has uncovered massive bribery and embezzlement in Brazil's elite - with Temer's probe being just the latest offshoot.