The Trump administration is reportedly amping up its investigation into Hillary Clinton’s private emails — reviving a controversial topic that dominated headlines during the 2016 presidential election and one that President Donald Trump continues to mention.

The Washington Post reported on Saturday that the State Department is investigating the email records of dozens of current and former officials who sent messages to Clinton’s private email account when she was secretary of state. The New York Times confirmed the continuation of the investigation on Sunday.

State Department investigators began contacting officials about the emails some 18 months ago, the Post reported. But the effort was apparently dropped before being revived in August.

“As many as 130” officials have been contacted by the Trump administration since then, the paper said, adding that “those targeted were notified that emails they sent years ago have been retroactively classified and now constitute potential security violations.”

The emails were largely sent between 2009 and 2013, when Clinton was secretary of state under former President Barack Obama.