The State Department has reportedly ramped up its investigation into former Secretary of State Hillary Clinton's private email server, an issue that took center stage during the 2016 presidential election.

According to the Washington Post, the State Department has called in 130 officials who had access to Clinton's email inbox. The officials ranged from low-level employees to senior officials who reported directly to Clinton. Former aides were sent letters letting them know that their emails were retroactively deemed "classified" and sharing that information could be deemed a security violation.

The investigation began 18 months ago, fizzled out and then was picked back up in August. Senior officials at the Department say they have followed standard protocol. Because the investigation began in the later days of the Obama administration, it is just now coming to an end.

Former Obama officials have said the probe is taking place for political gains.

“I’d like to think that this is just routine, but something strange is going on,” said Jeffrey Feltman, a former assistant secretary for Near East Affairs.

Feltman received a letter early last year from the Department making him aware that six of his emails included classified information. A couple weeks ago he received another letter, this one telling him he was responsible for more sending more than 50 emails that had classified information.

“A couple of the emails cited by State as problems were sent after my May 2012 retirement, when I was already working for the United Nations,” Feltman said.

Current state officials say the investigation has nothing to do with who is in office.

“This has nothing to do with who is in the White House,” an anonymous senior State Department official told the Post. “This is about the time it took to go through millions of emails, which is about 3½ years.”

“The process is set up in a manner to completely avoid any appearance of political bias,” a second official told the Post.

The investigation into Clinton's use of a private server for emails began in July of 2015 and wrapped up one year later. Then-FBI Director James Comey closed the case with no charges. Although he said Clinton and her aides' conduct was "extremely careless," it wasn't criminal.