Sacramento, California - California's Governor Gavin Newsom hit back Tuesday at US Justice Department claims that federal investigations into him and his entourage were long-standing, insisting he was being targeted at Donald Trump's behest.

Newsom, a likely Democratic White House contender in 2028, accused the Republican president on Monday of launching a criminal investigation into him and his wife, Jennifer Siebel Newsom, as a "personal vendetta."

A source at the Department of Justice in Washington told AFP this was not the case, insisting the probes were not initiated by "main Justice" but were begun about a year ago by the Sacramento-based US attorney for the Eastern District of California after being triggered by information from whistleblowers.

The source, who requested anonymity, said the investigations were focused on "tax activity" involving Newsom's wife, a documentary filmmaker, and activities related to his former chief of staff and possibly current aides.

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Dana Williamson, a former Newsom chief of staff, pleaded guilty in May to bank and wire fraud and other felony charges stemming from a position she held prior to working for the governor.

In a media release on Tuesday, Newsom slammed the attempt by "anonymous" sources to muddy the waters.

"Note DOJ's specific and consistent use of the word 'originated' in their anonymous media statements yesterday," the statement said.

"Under Donald Trump, the DOJ has shown a willingness to seize on virtually ANY allegation – no matter how flimsy (see, for example, the investigation into [former Federal Reserve chief] Jerome Powell) – as a pretext for political appointees to then weaponize the justice system against the President's enemies."

Newsom, in a video on Monday, said federal agents had questioned friends and associates of him and his wife and have been sifting through "years and years of random documents."

"Donald Trump isn't just coming after me because of my mean tweets," Newsom said. "He's coming after me because I am considering running for president."

"To get me, he's coming after my wife," he said. "One by one, anyone who has challenged Donald Trump has ended up on his hit list."