A former top Hillary Clinton Hillary Diane Rodham ClintonBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Virginia Democrat blasts Trump's 'appalling' remark about COVID-19 deaths in 'blue states' The Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally MORE aide says President-elect Donald Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE is worried about his legitimacy.

“I think Donald Trump is trying to cling to whatever legitimacy is still in effect here,” Brian Fallon, Clinton's former press secretary, said Friday on CNN’s “New Day."

Fallon called Trump's critical tweets about Clinton earlier Friday "just the latest indication that Donald Trump is someone who’s very insecure in his victory. And I understand why.”

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“Every day there are new developments, new shoes dropping, so to speak, that call into question the legitimacy of his win," he said.

Fallon pointed particularly to intelligence reports about Russian interference in the presidential election, as well as questions about how public announcements by FBI Director James Comey's affected the result.

Trump earlier Friday tweeted that the FBI had been more than fair to Clinton.

“What are Hillary Clinton’s people complaining about with respect to the FBI?” Trump asked. "Based on the information they had she should never have been allowed to run – guilty as hell. [The FBI] were VERY nice to her. [Clinton] lost because she campaigned in the wrong states – no enthusiasm!”

The Justice Department inspector general on Thursday announced it would investigate the FBI’s conduct leading up to the 2016 elections.

Clinton’s campaign has blamed Comey’s public remarks about the investigation into her private email server for costing her the election.