A retired four-star Army general said that he believes that President TrumpDonald John TrumpTrump calls Sri Lankan prime minister following church bombings Ex-Trump lawyer: Mueller knew Trump had to call investigation a 'witch hunt' for 'political reasons' The biggest challenge from the Mueller Report depends on the vigilance of everyone MORE is a “serious threat to US national security.”

Retired Gen. Barry McCaffrey tweeted Friday that he reached the conclusion about Trump because the president “is refusing to protect vital US interests from active Russian attacks.”

“It is apparent that he is for some unknown reason under the sway of [Russian President Vladimir] Putin,” he added.

 

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McCaffrey has also worked as an adjunct professor at the U.S. Military Academy and led the White House Office of National Drug Control Policy for five years during the Clinton administration.

Trump has come under fire for his response to Russian interference in the U.S. election. The president has repeatedly hit the probe into Russia's election meddling as a "witch hunt."

His administration unveiled new sanctions against Russian cyber groups involved in election meddling on Thursday, including individuals and groups charged with election interference by special counsel Robert MuellerRobert (Bob) Swan MuellerSasse: US should applaud choice of Mueller to lead Russia probe MORE.

However, Trump had been criticized for not implementing sanctions against Russia earlier, after Congress passed a bipartisan bill last year giving him the power to do so.

U.S. Cyber Command chief and National Security Agency Director Adm. Michael Rogers testified before the Senate last month that he hadn’t received instructions from Trump to take additional steps to deter Russian cyberattacks aimed at U.S. elections.