In the midst of all of the talk of Russia and Ms. Yates’s warnings about Mr. Flynn, Senator Ted Cruz of Texas, a former Republican presidential candidate, steered the hearing toward the email issue. He asked Mr. Clapper what he would do if, hypothetically, his employee forwarded emails containing classified information.

The question was a thinly veiled reference to Huma Abedin, an aide to Mrs. Clinton, forwarding emails containing classified information to her husband, Anthony D. Weiner, a former New York representative. Mr. Comey said Ms. Abedin forwarded the messages for Mr. Weiner to print for her to give to Mrs. Clinton.

Several current and former government officials familiar with the investigation into Mrs. Clinton’s handling of delicate information said that while some emails had been forwarded, a vast majority were instead backed up to Mr. Weiner’s computer.

Mr. Clapper did his best to keep on his game face — and to stick to the hypotheticals.

“It raises all kinds of potential security concerns, again depending on the content of the email, what the intent was, a whole bunch of variables here would have to be considered,” Mr. Clapper said. “But given a hypothetical scenario, I’d be quite concerned.”

5. You can learn a lot from the news media.

Ms. Yates’s brief tenure as acting attorney general came to an abrupt end on the evening of Jan. 30 when she refused to defend Mr. Trump’s executive order barring refugees and travel from several predominantly Muslim countries.

On Monday, Ms. Yates said the order came as a surprise to her. “Not only was the department not consulted, we weren’t even told about it,” she said. “I learned about this from media reports.”

She then defended the decision that got her fired, explaining that she could not defend the order largely because Mr. Trump himself had indicated that it was intended to single out Muslims. Federal judges have since made similar findings as the case winds through the courts.