Given that Congress's array of campaign finance laws are designed to prevent precisely what the Clinton Foundation has wrought -- namely, the appearance of political influence on sales -- one would think the FBI and the Justice Department would be obliged to investigate.
But from what I understand of the law, there's no such obligation. I believe those things are usually at the discretion of the government. McCarthy probably knows that too but this is just his way of saying, "Hey guys and gals, this is pretty damn serious."
Which brings me to a big problem with the criminal law. Applying it depends on government officials who rarely have the right incentives. In this case, the charge would be brought against the leading Democrat for President and it would have to be approved, most likely, by her former boss Barack Obama, whom her husband, Bill Clinton, campaigned tirelessly for. The incentives aren't exactly aligned in the direction of charging her with a crime. So I wouldn't give it a probability more than about 0.05, unless there's a strong grassroots campaign that cuts across party lines.
I know that David Friedman has written and spoken in the past about why he thinks we can do away with criminal law and have only civil law. I watched the whole of this fascinating and informative talk (it takes 40 minutes) to see if he addressed this kind of issue. Specifically, in a system of civil law, how would such a case be handled? Unfortunately he doesn't. Possibly he addresses it elsewhere.
The whole Hillary Clinton thing got me wondering, by the way, about my former Congressman Leon Panetta. He runs the Panetta Institute and that Institute took donations from "forward-looking companies" even while he was Director of the Central Intelligence Agency and Secretary of Defense. He recused himself at the time and turned over the running of the Institute to someone named Sylvia Panetta, i.e., his wife. While he was Secretary of Defense, the Institute took an $8,000 donation from defense contractor Lockheed Martin. Granted that is rounding error on the donations that the Clinton Foundation took, but still, it seems worth looking into.