The FBI probe into Hillary Clinton's private email server is the most worrisome issue now facing her Democratic presidential campaign, CNN reports.In a discussion about a new film based on Peter Schweizer’s book "Clinton Cash" about to debut at the Cannes Film Festival, CNN anchor John Berman asked correspondent Jeff Zeleny for his analysis on how the pay-for-play allegations would affect Clinton's White House bid.posted a clip of the exchange.There's not "a ton of smoking guns," Zeleny said of the book and movie.But the FBI investigation into Clinton’s sever while she served at the State Departmentcould go anywhere."I think the thing that worries the Clinton campaign the most are the things they can’t control," Zeleny said."They know everything that’s in this book. They know every word that’s in the movie … Every news organization has gone over that book. Yes, there are a lot of questionable things, but it isn’t all that new, but the emails, the FBI investigation, which we don’t talk about a lot, that is still hanging out there. That is the thing that worries the Clinton campaign because they cannot control what happens to that … The FBI investigation is not over yet, and they don’t know the ending."The movie goes into Schweizer’s book and its allegations against the Clinton Foundation's alleged slush fund. FBI Director James Comey has says there's no timetable for the completion of his probe, but has been critical of Clinton's description of the investigate as a "security inquiry." "It's in our name," he said last week about his Federal Bureau of Investigation.Related Stories: