"In the end, what causes an officeholder or politician to resign is one of three things," said Republican strategist John Ullyot, who was an adviser to former Republican senator John Warner. Ullyot said a collapse of public support, a triggering event such as an indictment, and knowledge that another shoe is about to drop are the three.
"Absent one of those three things, it's really hard to see where it is in his own interest to leave," Ullyot said of McDonnell.
In case you're just tuning into the story, here's where things stand: Wealthy businessman Jonnie R. Williams Sr. gave at least $145,000 to assist McDonnell and his family in 2011 and 2012, reports the Post's Rosalind S. Helderman, who has been on top of this story for months. Williams, the head of the dietary supplement manufacturer Star Scientific, gave to a corporation owned by McDonnell and his sister, spent thousands to cover catering costs at the wedding of McDonnell's daughter, and gave other undisclosed gifts to the family, among other things, all as McDonnell and his wife took steps to promote his company and its products.
McDonnell's office has said the governor has been diligent about filling out the necessary disclosures. And the governor has said his and his wife's efforts to boost Williams's company have been in line with that they would do for any Virginia business. Still, state and federal authorities are looking into the matter.
"Star Scientific and Jonnie Williams have not received any board appointments, economic development grants, targeted tax incentives or government contracts during this administration," said McDonnell spokeswoman Taylor Keeney. "The governor has been diligent over the years in making his financial disclosures.
On Wednesday, state Sen. Barbara Favola (D) called on McDonnell to resign. But most Democratic leaders haven't gone that far. McDonnell hasn't faced widespread calls from Republicans to hit the road, either.
Polling shows the public isn't up in arms, nor are they tuning in to the story very closely. McDonnell's approval stood at 62 percent in a Washington Post poll released in early May. And 59 percent said they think he has high personal and moral and ethical standards. When it came to the Star Scientific story, only 32 percent said they were following it closely, including just 9 percent who said they were following it very closely.
For his part, McDonnell has shot down rumors that he might be stepping aside. “I don’t know where these things are coming from. Some of the press accounts have been completely out of control, about rumors, about resignation and so forth,” McDonnell told WTVR on Tuesday.
What comes from the investigations into McDonnell is what will really determine his fate, observers say.
"I don't think he has to resign unless there is sort of indictment brought down, something like that," said Christopher Newport University political scientist Quentin Kidd. "I think then it would be nearly impossible for him to stay in office."
The fact that McDonnell's activities are under investigation has limited his ability to get out in front of the story, said one experienced Democratic strategist.
"When you've got to put your legal needs ahead of the public desire and right to hear form you, then I think you are in a very, very precarious situation," said Democratic strategist Mo Elleithee.
The other variable is whether electoral considerations will prompt Republicans to press McDonnell to step down, fearful he will be an albatross heading into the fall campaign. But the lack of competitive races for the state House of Delegates could limit the extent to which McDonnell is used as a negative.
"You have a lot of safe Republican seats, number one," said Ullyot. "Number two, when it comes to the governor's race, and state legislative issues, this is really seen as a personal issue."
Attorney General Ken Cuccinelli II, the Republican nominee for governor, declined Thursday to say whether he thinks McDonnell should resign. But he acknowledged the issue has become a "distraction" in his race, as he fielded questions about gifts he took from Williams.
"I do think there will be a lot of a pressure to distance themselves in a very aggressive way," Eleitheee said of Republicans running for office in Virginia.
The fact that McDonnell is so near to the end of his term supports the idea that he can make it to the finish line. But even if he does, his once promising prospects for national office or a position in a Republican administration have clearly taken a big hit.