When Monica Lewinsky testifies before the grand jury as soon as this week, there's only one issue that really matters: her credibility.
Like a blinking neon sign, the credibility question has been flashing since the world first learned of this former White House intern with the sporty beret.
In the now-famous tapes that Linda Tripp made of conversations with Ms. Lewinsky, she reportedly said: "I have lied my entire life."
And the man who was defending her last winter, attorney William Ginsburg, intimated she is the kind of person who talks a lot and "may tell fibs, lies, exaggerations, oversell."
This is not a history that makes for the strong witness that independent counsel Kenneth Starr needs as he investigates whether President Clinton lied under oath about a sexual relationship with Lewinsky, or urged others to lie.
Now Lewinsky has received full immunity in exchange for recanting her sworn January affidavit in which she categorically denied having a sexual relationship with the president.
She has also reportedly agreed to testify that she and Clinton hypothesized about how to cover up their relationship, but not that he directly told her how to testify about it or that he urged her to lie about it under oath.
The big question
Is she believable?
The clincher for her story is her blue cocktail dress, whisked off to the FBI labs at the end of last week for DNA testing. If the results come out positive, and if they match the president's DNA - and those are still big ifs - her tall-tale rap will be a nonissue. Mr. Starr will have finally found his smoking gun.
"But short of the dress, the only issue is her credibility," says Susan Fain, a professor of criminal law at American University here.
The reason Starr needs Lewinsky to persuade the grand jury and prosecutors - and ultimately Congress - she's credible is that she's at the center of the controversy. She knows what happened. And, if this is to be more than just a "he said, she said" case, she needs to convincingly corroborate the testimony of the roughly 70 witnesses that have testified so far.
For instance, she knows what Clinton friend and adviser Vernon Jordan said to her about finding a post-Pentagon job in New York. Mr. Jordan and the president have different versions about that aspect of this case. The job assistance might be viewed as an incentive to hush up the talkative Lewinsky.
She also could corroborate whatever presidential secretary Betty Currie has said about Lewinsky's 37 visits to the White House since she stopped working there in May 1996. In his Paula Jones deposition, the president said Lewinsky came to the White House to visit Ms. Currie.
And she can provide the explanation about the gifts the president gave her, gifts that were returned to Currie after Lewinsky found out she had been subpoenaed in the Paula Jones case.
Robert Pugsley, a criminal-law professor at Southwestern University School of Law in Los Angeles, argues that Clinton's credibility is far worse than Lewinsky's. Other than her affidavit, "she's been consistent in [saying] there was a sexual relationship."
The president, on the other hand, did not tell the truth about his relationship with Gennifer Flowers, and a CNN/Time poll says at least 60 percent of Americans believe Clinton is not telling the truth now.
As Lewinsky prepares for her testimony, Starr's office and her own attorneys each have their own goals, explains Ms. Fain.
The prosecutor's aim is to get her to match what others who have gone before her have said - especially in the more damaging area related to obstruction of justice - thus building his case through corroboration.
Her own attorneys, meanwhile, need to make sure she's telling the truth - since her immunity deal goes up in smoke if she is found to be lying to this grand jury.
What her attorneys don't want is some new version that will raise doubts about her believability in the prosecutor's mind.
This is why, explains Fain, immunity deals produce an "incentive to conform one's story to what fits with what the grand jury has already heard, and that's not necessarily an incentive to the truth itself." The only interest of Lewinsky's lawyers, she says, "is that Starr is happy with her testimony and he doesn't try to claim that she has perjured herself in front of that grand jury, [making] the immunity agreement ... invalid."