Clinton Emails
Clinton Emails

The Federal Bureau of Investigation is drawing heated criticism for inserting itself into the U.S. presidential campaign after the bureau's director announced he was reviving the investigation into Hillary Clinton's email practices.

Federal agencies historically have tried to stay out of partisan politics to preserve their independence and authority, but this year the FBI has been drawn into examining both of the leading candidates.

For Clinton, the bureau announced Friday it is reviewing a new set of emails that could lead to more information about how Clinton, the Democratic presidential nominee, handled sensitive information in emails when she was the country's top diplomat from 2009 to 2013.

FBI Director James Comey previously closed an investigation into Clinton's handling of the classified material in July, declaring that she was "extremely careless" in dealing with the documents, but that no criminal charges were warranted.

WATCH: Clinton Talks about the FBI Investigation

With its review of the latest batch of Clinton's emails, the FBI is trying to determine whether they contained classified information and if they include evidence that shows whether attempts were made to conceal the emails from investigators.

Trump and Russia

Clinton's Republican rival, Donald Trump, also has caught the eye of FBI investigators.

Agents investigated possible links this summer between Trump advisers and Russian financial figures. When investigating the hacking into Democratic emails, the FBI looked into whether the cyberattacks were attempts by the Russians to influence the presidential election in Trump's favor. The bureau also investigated a possible confidential channel of email communication between the Trump Organization, Trump's private business conglomerate, to a Russian bank.

None of the probes yielded any conclusive evidence that Trump is directly linked to the Russian government. And the FBI now believes the hacking into Democratic emails was a Russian attempt to disrupt the election, instead of an attempt to get Trump elected.

WATCH: Trump Talks about Russia

Comey’s actions ‘inexplicable’

Kenneth Gross, a former head of enforcement at the Federal Election Commission, told VOA that Comey's revival of Clinton's email controversy only days before the presidential election has created a situation that is "almost unconscionable."

Gross said the FBI director made a "series of mistakes" going back to July when he criticized Clinton as being "extremely careless" for her handling of emails before concluding she did nothing illegal, and then left open the possibility he would report back to Congress if there were new developments.

"I'm not saying he shouldn't look at the additional emails, but certainly the idea that he would raise the specter of any kind of conduct that would raise legal issues within 11 days of the election … is just inexplicable," said Gross, who now heads the political law practice at the law firm Skadden Arps.

It is "hard to even explain what was going on other than him being concerned about covering his own butt," he added.

Comey and Hoover

Gross does not believe Comey's actions are part of a political conspiracy, nor does he believe the FBI director violated the federal Hatch Act, which states, in part, that its aim is to "ensure that federal programs are administered in a nonpartisan fashion."

Since Comey's Friday announcement about Clinton's use of emails, some critics are comparing him to J. Edgar Hoover, who ran the FBI and its predecessor from 1924 to 1972. Some historians have accused Hoover of trying to influence the presidential election in 1948 by secretly giving the campaign of Republican presidential candidate Thomas Dewey information about Dewey's Democratic rival and incumbent President Harry Truman, who nevertheless won what is widely viewed as the greatest election upset in American history.

Gross believes the comparisons of Comey to Hoover are inappropriate because, unlike Hoover, Comey's actions have been public and related to official agency business.

"The effect could be as damaging," Gross said, "but I don't think what Comey was up to compares to what Hoover was up to."