"Focus on the only potential eye witness," said another. "Where is Mark Judge?"

"This damages his credibility, perhaps irrevocably," said one former Justice Department prosecutor.

Brett Kavanaugh, President Donald Trump's embattled nominee to fill a Supreme Court seat, came out swinging when he defended himself Thursday against a bombshell allegation of sexual assault.

But the most salient piece of evidence came not from what Kavanaugh said, but what he didn't say.

At the center of Thursday's hearing is an accusation of sexual assault that Dr. Christine Blasey Ford, a professor at Palo Alto University, made against Kavanaugh earlier this summer and which became public last week.

Testifying to the Senate Judiciary Committee, Ford said Kavanaugh attacked her when they were at a high school gathering in the summer of 1982. She also said that Kavanaugh's friend, Mark Judge, witnessed the alleged assault and at times egged Kavanaugh on.

Kavanaugh vehemently and categorically denied Ford's allegations on Thursday.

But he became visibly evasive when Democratic lawmakers on the Senate Judiciary Committee asked him two pointed questions: would Kavanaugh be in favor of Judge testifying before the committee, and would he ask the White House to order the FBI to investigate the claims against him?

When Vermont Sen. Patrick Leahy asked Kavanaugh whether he wanted Judge to testify, Kavanaugh replied: "He's already provided sworn testimony," referring to an affidavit Judge submitted which was signed by his lawyer.

When Illinois Sen. Dick Durbin asked Kavanaugh whether he would support an FBI investigation into Ford's claims and Judge appearing before the committee, Kavanaugh said that the FBI "does not reach conclusions" and dodged Durbin's inquiries about Judge.

"You can't have it both ways," Durbin told Kavanaugh. "You can't say here at the beginning ... 'I welcome any kind of investigation,' and then walk away from this."

"This thing was sprung on me," Kavanaugh said. "This thing was sprung at the last minute after being held by staff, you know, and I called for a hearing immediately."

Durbin replied: "Judge, if there's no truth to her charges, the FBI investigation will show that. Are you afraid they might not?"

Kavanaugh then accused Durbin of asking a "phony question," saying that the FBI would "just go and do what you're doing: ask questions and then type up a report. They don't reach the bottom-line conclusion."

But during his opening statement, Kavanaugh touted the background checks the FBI had conducted on him when he was up for other jobs within the US government earlier in his career, which he said found no evidence of any wrongdoing in his past.

A 'straw man argument'

Christine Blasey Ford claims Mark Judge aided in an alleged sexual assault involving Supreme Court nominee Judge Brett Kavanaugh at a high school party in Maryland when they were teenagers. Michael Reynolds/Getty Images

Throughout the hearing, at least five Democratic lawmakers asked Kavanaugh about opening an FBI investigation on at least nine different occasions. Each time, he declined to give a yes-or-no answer.

Meanwhile, Republicans on the panel asserted that the FBI did not need to investigate the allegations because the committee was conducting an inquiry into them.

Jeffrey Cramer, a longtime former federal prosecutor in Chicago, characterized the claim as a "straw man argument."

"FBI finds potential eyewitnesses, tries to confirm surrounding facts," and more, he said. "Kavanaugh and the sex-crimes prosecutor asking questions would both agree that they would want to talk to any potential witnesses before reaching any conclusions. Any rookie prosecutor, or investigator, or finder of fact, would talk to Mark Judge. A court would do so under oath."

Durbin later brought up Ford’s testimony, during which she said that she ran into Judge at a local supermarket six to eight weeks after the alleged assault. Durbin said that if the committee subpoenaed Judge to testify, lawmakers could get answers on some of the specifics of the event that Ford said she could not recall.

"So the point I’m getting to is, we at least can connect some dots here and get some information," Durbin said. "Why would you resist that kind of investigation?"

Kavanaugh repeated that he wanted a hearing before the committee as soon as the allegation became public last week. He did not say whether he wanted his friend to testify.

"He complains about delays & says [Mark] Judge submitted an affidavit, but refuses to agree he should testify & be subjected to cross examination," wrote the former federal prosecutor Joyce Vance. "This damages his credibility, perhaps irrevocably."

"He asserts the truth in a prepared statement but can’t seem to handle questions he has to have known were coming," she added.

Cramer echoed that view and highlighted Judge's importance in the hearing.

"Democrats should say the name Mark Judge in every question," he said. "How far was Mark Judge from you and Brett? Where was Mark Judge standing? Did Mark Judge say anything? Did you make eye contact with Mark Judge while being pinned down by Brett?"

Ford said during the hearing that the sharpest memory she had of the attack was the "uproarious laughter" Judge and Kavanaugh allegedly shared at her expense.

"They both seemed to be having a good time," Ford said in her opening statement. "Mark was urging Brett on, although at times he told Brett to stop. A couple of times I made eye contact with Mark and thought he might try to help me, but he did not."

Legal scholars and those who observed the testimony from both sides of the aisle said Thursday that they found Ford to be a credible witness.

Kavanaugh was "certainly forceful until it comes to the FBI asking questions or Mark Judge testifying," Cramer said.

"An affidavit, as the judge knows, is meaningless. Democrats' questions are weak but targeted. Focus on the only potential eyewitness. Where is Mark Judge?"