"I don't believe our democracy can function for long on lies, particularly when inconvenient and hard facts spoken by the practitioners of truth are dismissed as 'fake news, '" Clapper writes.
Nielsen, who was reported earlier this month to have considered resigning over criticism from Trump regarding immigration policy, said she generally had no reason to doubt any intelligence assessment.
"I want to be very clear what we have seen the Russians do is attempt to manipulate public confidence on both sides".
Nielsen's statement appeared to directly contradict the findings of a 2017 intelligence assessment on Russian meddling in the 2016 presidential election that concluded Putin was interested in hurting Clinton's chances and later helping those of Donald Trump.
Donald Trump would have been on his way to losing the 2016 election without help from Vladimir Putin and the Russians, former Director of National Intelligence James Clapper claims.
"This report is over a year old, has stood the test of time, was agreed to by the entire Intelligence Community, and was backed up by Senate investigators", he said in a statement. "I think what they are trying to do is to disrupt our belief and our own understanding of what's happening".
She made the remarks in response to a reporter's question after holding a classified meeting on 2018 election security with members of the House of Representatives. "Central Intelligence Agency and Federal Bureau of Investigation have high confidence in this judgment; NSA has moderate confidence". That was at odds with Republican members of the House intelligence committee, who said that while Russian President Vladimir Putin wanted to hamper Hillary Clinton's campaign, that didn't mean he wanted to help Trump.
After Nielsen's remarks Tuesday, DHS press secretary Tyler Houlton released a statement saying, "The Secretary has previously reviewed the Intelligence Community's assessment and agrees with it - as she stated today and previously", adding, "Russian goals included undermining faith in the United States democratic process and harming a candidate's electability and potential presidency".
On Tuesday, he criticized the president for demanding the Justice Department investigate allegations that the Federal Bureau of Investigation placed a mole in the Trump campaign.
But the Senate Intelligence Committee, in a bipartisan fashion, recently affirmed the conclusion.
The spokesman added that the language of the intelligence community's assessment is "nuanced" and said that the reporter's question "did not reflect the specific language in the assessment itself". Mark Warner (D-Va.) sent an email to reporters with several links to the intelligence community's findings.