One by one, her campaign's arguments that the probe is partisan and part of the "vast right wing conspiracy" against her have fallen apart as both the Justice Department and State Department have opened probes into her use of the email server and the handling of classified information by her aides Huma Abedin and Cheryl Mills. The FBI is reportedly using 150 agents to investigate criminal activity.

Hillary Clinton's mishandling of classified information by using her private, unsecured server to store sensitive documents makes it look more and more as though a criminal case is being developed against her by the FBI.

Andrew McCarthy sums up her potential legal problems:

"If the press reporting is to be believed, [the case] looks very strong," McCarthy said. "I say that because the statutes involving mishandling classified information are very prosecution-friendly, and they're obviously intended to be that way." McCarthy points to the case of retired Gen. David Petraeus as an example. Petraeus pleaded guilty to a misdemeanor charge in April last year after sharing printed classified documents with a woman who was his biographer and mistress. Observers have drawn parallels between the Petraeus and Clinton cases, both of which involved the unauthorized disclosure of classified material. "I was a critic of the Petraeus prosecution, because I thought he got a slap on the wrist," McCarthy said. "When Congress enacted these laws, the idea was to give the maximum amount of protection the criminal law could give to national defense secrets." But a growing number of skeptics fear that, even if the FBI were to recommend an indictment, the Justice Department's leadership would decline prosecution of the likely Democratic nominee for political reasons. "I'm very confident that the the FBI is going to do a thorough investigation and that if there's an airtight case to be made, they'll make it," McCarthy said. "What I'm not confident in is whether the Obama Justice Department will authorize the energetic use of a grand jury and, ultimately, an indictment." "I know it's nominally Attorney General [Loretta] Lynch's call," he added. "But I think it's ultimately President Obama's call."

This is common thinking outside the Beltway: that Obama will order Lynch to stand down. I think a more likely scenario is a Petraeus-type prosecution, where a plea deal is carefully negotiated, and she gets away with a slap on the wrist, no jail time, and a hefty fine.

But other observers think the case is too strong for a mild response by the government:

Joseph DiGenova, a former U.S. attorney under President Ronald Reagan, told the Examiner in January that Lynch would have "no choice" but to indict Clinton if the FBI recommended an indictment. That recommendation would come in the form of a confidential memo, DiGenova said, but "the bureau will no doubt let it be known" that such a memo exists in order to increase the public pressure on Lynch to proceed with the case. Most reports indicate FBI agents are looking into whether Clinton or her staff violated provisions of the Espionage Act that cover the treatment of sensitive information, an offense that can carry a sentence of up to 10 years in prison. While a number of factors are at play in the unusual case of Clinton's emails, McCarthy said the former secretary of state could be looking at more than one felony charge.

So what happens if DoJ pulls the trigger and actually goes through with an indictment?

If the Justice Department hits Clinton with criminal charges, she faces a difficult decision: withdraw her name from the Democratic primary, or continue to fight the perception of wrongdoing in the court of public opinion while hoping a court of law does not find her guilty. "There's no legal reason why she'd have to drop out," Mukasey said. "The Constitution lists the qualifications for the presidency. And if you add anything else, it would be unconstitutional." But most observers agree Clinton would struggle to remain in the race if a grand jury indicted her. At the very least, strategists say, the charges would invite another Democratic challenger into the primary and upend what still looks to be a relatively clear path to the nomination for Clinton. Mark Jones, a political science fellow at Rice University's Baker Institute, said Clinton would most likely exit the race if indicted. "If she withdraws, then effectively she can relieve all of her delegates from their pledge" to support her at the Democratic National Convention in July, Jones said.

Timing is everything. Clinton is expected to be so far ahead at the end of March that no challenger would realistically be able to catch her. Suppose an indictment came down between the time she clinched the nomination and the convention. Does anyone really see Hillary Clinton surrendering the nomination because she's been indicted?

What happens if she's indicted later this summer, after the convention? That would really open a can of worms, because by then, most states will have printed up their ballots, and the Democrats would be hard pressed to get a candidate on enough ballots to run a credible campaign.

That's the ultimate Democratic Party nightmare scenario.