Rupert Murdoch suggested Sunday on social media that the White House has some alternatives lined up for the Democratic presidential nomination in the event that Hillary Clinton is further engulfed in her email scandal.

"Hillary email troubles get really serious," Murdoch wrote on Twitter. "WH has surprising alternates if things get worse."

Since before launching her second campaign for her party's nomination last year, Clinton has faced scrutiny over her exclusive use of a private email server to conduct official government business while she was secretary of state.

Critics have charged her with jeopardizing national security while Clinton has said she never used the email server to relay confidential information.

The State Department on Friday, however, marked 22 of her emails "top secret" and refused to release any part of them to the public, a major step in a months-long process of reviewing Clinton's personal records.

Also on Friday, White House spokesman Josh Earnest said the Obama administration is "not worried" about a potential indictment of Clinton.

Murdoch, whose sprawling corporate media empire includes the Wall Street Journal and Fox News, did not elaborate on who the White House might favor as a successor for the Democratic nomination.

Vice President Joe Biden has, however, ruled out a run.