There were cheers, laughs, and plenty of smiles a day after City Council Speaker Corey Johnson and Mayor Bill de Blasio shook hands on a city budget deal. They took a victory lap together Tuesday, appearing an event celebrating half-price MetroCards for low-income New Yorkers and stopping by a rally in support of a funding boost for affordable housing for seniors.

"Fairness means all the good people of this city can afford to live in their own city," the mayor said.

But the good will between the two sides of City Hall may not stick around long. Questions are lingering about who knew what — and when — at the city's public housing authority and at City Hall.

"This is very, very serious stuff," Johnson said to members of the news media Tuesday. "People's lives are being endangered."

Federal prosecutors issued an 80-page complaint Monday detailing shocking, and potentially criminal, levels of negligence and outright deception about conditions in public housing.

"If anyone is found breaking the law, they must be terminated! Immediately!" Johnson said. "No one can hold a job if they are endangering the life and safety of children and public housing residents."

The city council can hold hearings to demand more answers about the authority's failure to conduct lead paint inspections, and the elaborate lengths, according to the complaint, employees went to in order to hide deteriorating conditions from federal inspectors.

The speaker says he needs to consult with other council members before deciding how to proceed with any hearings or other action in response to the accusations against NYCHA.