Rep. Adam SchiffAdam Bennett SchiffRepublicans consider skipping witnesses in Trump impeachment trial Trump rails against FBI, impeachment during Pennsylvania rally Democrats reach cusp of impeachment MORE (D-Calif.) said Sunday that FBI Director James Comey's email to lawmakers regarding the Hillary ClintonHillary Diane Rodham ClintonTrump trade deal likely to sow division in Democratic presidential field Trump supporters at Pa. rally 'upset' after Democrats introduce impeachment articles Hillary Clinton documentary to premiere at Sundance 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.