Dershowitz, who helped advise O.J. Simpson's defense team, said Lerner "should never have been allowed" to make her opening statement.
"You can't simply make statements about a subject and then plead the Fifth in response to questions about the very same subject," Dershowitz said. "Once you open the door to an area of inquiry, you have waived your Fifth Amendment right... you've waived your self-incrimination right on that subject matter."
House Oversight Committee Chairman Darrell Issa (R-Calif.) indicated he could be willing to pursue forcing Lerner to testify.
“Ms. Lerner may have waived her Fifth Amendment rights by addressing core issues in her opening statement and the authentication afterwards,” Issa said Wednesday. “Although I excused Ms. Lerner subject to a recall, I am looking into the possibility of recalling her and insisting that she answer questions in light of a waiver.”
But Rep. Elijah Cummings (D-Md.), the ranking Democrat on the panel, noted the committee hearing was "not a courtroom."
“In a courtroom that might have been the case. It’s a legal question," he said.
Dershowitz said the "law is as clear as it could be" on the subject.
"Once you open up an area of inquiry, you can't shut off the spigot – that's the metaphor that the Supreme Court has used," he said.