Rep. Adam SchiffAdam SchiffOvernight Cybersecurity: Equifax hit by earlier hack | What to know about Kaspersky controversy | Officials review EU-US privacy pact Democrat: Trump only loyal to the 'pro-Trump' party Sunday shows preview: Trump officials gear up for UN assembly MORE (D-Calif.) said Sunday that FBI Director James Comey's email to lawmakers regarding the Hillary ClintonHillary Diane Rodham ClintonBiden slams Trump over golf gif hitting Clinton Overnight Cybersecurity: Equifax hit by earlier hack | What to know about Kaspersky controversy | Officials review EU-US privacy pact Overnight Tech: Equifax hit by earlier undisclosed hack | Facebook takes heat over Russian ads | Alt-right Twitter rival may lose domain MORE email server investigation was "a terrible error in judgment."

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"I think this was a terrible error in judgment by the director, to release this kind of ambiguous letter. These may be pertinent; they may be significant; they may not be significant. They may not be pertinent," Schiff, the ranking member of the House Intelligence Committee, told ABC's "This Week."

On Friday, Comey sent a letter to Congress alerting lawmakers to the fact that the FBI discovered emails that may be relevant to the Democratic presidential nominee's server investigation.

It was later reported that the separate investigation was into former Rep. Anthony Weiner (D-N.Y.). Weiner is the husband of longtime Clinton aide Huma Abedin.

"That kind of an ambiguity bomb this close to an election was a terrible lapse in judgment," Schiff added.