But now that he has lost support from nearly all his allies in the state capitol — both the House and Senate Democratic caucuses have urged him to quit — it is not clear how long Mr. Northam can last. He will have a difficult time recruiting businesses to the state and could also face challenges raising campaign contributions, which is crucial given that all 140 seats of the state legislature are on the ballot this fall and Democrats need to win only a handful of races to take control of both chambers.

Further, Mr. Northam is confronting a national party that will not ease up on him.

Democrats in the Trump era have adopted a sort of zero-tolerance approach in their ranks toward misconduct involving race and gender. With Republicans eager to level accusations of hypocrisy, Democratic leaders in Washington have sought to aggressively police the sort of misdeeds they have linked to Mr. Trump. They have pushed out lawmakers such as former Senator Al Franken of Minnesota and former Representative Ruben Kihuen of Nevada, both of whom were accused of sexual harassment.

With the 2020 Democratic presidential primary race getting underway, the pressure on Mr. Northam has been even more intense: The party’s White House hopefuls were some of the first officials to call on him to resign Friday night, beginning a cascade of demands that extended through the day Saturday.

Calls for Mr. Northam’s resignation also came from state Democrats like former Gov. Terry McAuliffe and Mayor Levar Stoney of Richmond, both longtime allies of the governor. By the end of the day, Mr. Northam had few public allies left beyond his own staff and some longtime friends, like the Rev. Kelvin F. Jones, an African-American whose Baptist church Mr. Northam attends when he is on the Eastern Shore.

“We cannot destroy somebody’s life for a choice we perceive they made,” said Mr. Jones, who traveled to Richmond on Saturday to be with the governor and said he did not think it was Mr. Northam in the picture.

The Virginia Constitution allows the impeachments of governors for “offending against the Commonwealth by malfeasance in office, corruption, neglect of duty or other high crime or misdemeanor.” If Mr. Northam chooses to remain in office and legislators ultimately seek his impeachment, the House of Delegates would be the first legislative chamber to consider the matter. The Senate would conduct any subsequent trial and determine whether Mr. Northam kept power.