"The message of the US government is clear: the American people, not a foreign power decide the outcome of [the election], not Iran and its malicious cyber activities as laid bare in today's indictment," he added.
The charges in the grand jury indictment have not been released.
The employee came forward with new information weeks before the new indictment was returned in July.
"I personally think that they probably have the basis for legitimately indicting the president."
More than $100,000 in gold bars were discovered in Menendez's home by FBI agents during a raid, according to the indictment of the senator.
The former president is due Tuesday at a Manhattan courthouse where supports have gathered protest in indictment.
"A Trump indictment would be a disgusting abuse of power. The DA should be put in jail," he wrote.
The indictment comes amid increased scrutiny regarding national security threats and a series of incidents regarding Chinese nationals trespassing on U.S. military grounds.
The charges were included in newly unsealed federal indictment in Manhattan
Sopko's agency indicted and convicted over 150 people for waste, fraud and abuse, and was able to return $4 billion to taxpayers.