The Department of Homeland Security's cyber chief, who presided over an elaborate election security effort guarding against foreign interference and fraud, was ousted by President Donald Trump on Tuesday as part of a continuing post-election purge of top national security officials.

Trump announced the dismissal in a tweet Tuesday night.

The dismissal of Christopher Krebs, director of DHS's Cybersecurity and Infrastructure Security Agency, follows the agency's declaration that the general election was the most secure in U.S. history.

The statement served as a pointed rebuke to a president who continues to make unsubstantiated allegations of voting fraud while Trump's legal team pursues multiple legal challenges in battleground states.

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"There is no evidence that any voting system deleted or lost votes, changed votes, or was in any way compromised," the agency reported Thursday in an assessment joined by a coalition of election security groups, including the National Association of State Election Directors. "All of the states with close results in the 2020 presidential race have paper records of each vote, allowing the ability to go back and count each ballot if necessary. This is an added benefit for security and resilience. This process allows for the identification and correction of any mistakes or errors." 

Krebs had been an outspoken defender of the nation's election security apparatus in the months leading up to Election Day, even as Trump repeatedly warned of massive fraud that never materialized.

Krebs was expecting to be fired as recently as last week, sources told POLITICO.

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Trump's unsupported allegations gave life to conspiracy theories that Krebs' agency sought to knock down by publicly calling out false claims on its website.

Earlier this week, as states were engaged in critical canvassing efforts, CISA seized on "rumor" that election results could be changed by a single "bad actor."

"Robust safeguards, including canvassing and auditing procedures, help ensure the accuracy of official election results," the agency stated.

Before his appointment as the first director of CISA, Krebs served as the DHS' assistant secretary for Infrastructure Protection.

Afterward, Krebs moved to Microsoft focussing on the company's cybersecurity and technology policy.

Krebs joined DHS in March 2017, first serving as a senior adviser on cybersecurity and infrastructure protection.

In his role as CISA director, Krebs was tasked with safeguarding national cyber networks along with maintaining the country's essential operations in the face of increasing attempts by foreign adversaries to disrupt the government. The nation's vulnerability was made clear in 2016 when Russia sought to undermine the general election.