Mike Waltz is in the hot seat as the Senate kicks off his contentious confirmation hearing to serve as ambassador to the United Nations.

Waltz, who previously served as national security adviser to President Donald Trump, was removed from the role following a string of scandals. Most notably, Waltz accidentally added the editor in chief of the Atlantic, Jeffrey Goldberg, to a private Signal group chat with other administration officials where they discussed and coordinated an imminent airstrike against the Houthis in Yemen.

'I was hoping to hear you had some sense of regret.'

Although Waltz has taken full responsibility for the "embarrassing" slipup, "Signalgate" was the Democrats' cannon fodder of choice on Tuesday.

Democratic Sen. Chris Coons of Delaware pressed the nominee over the use of Signal to communicate about ongoing military operations, saying it is "not an appropriate, secure means of communicating highly sensitive information." Coons also asked Waltz if he had been investigated over the incident.

"The use of Signal, as an encrypted app, is not only authorized, it was recommended by the Biden-era CISA guidance," Waltz said in defense of the chat.

RELATED: Scott Jennings shreds media's narrative around Trump admin Signal group chat

Kent Nishimura/Bloomberg via Getty Images

"Of course, there was no classified information exchanged," Waltz added.

Coons reiterated his concerns over the "demonstrably sensitive information" that was leaked by the chat, asking Waltz again if he had been investigated for it.

"The White House conducted an investigation, and my understanding is that the Department of Defense is still conducting the investigation," Waltz said.

"At the time, you took responsibility for adding a journalist to the Signal chat," Coons said in response. "But it doesn't seem to me that the administration's taken any action to make sure this doesn't happen again. ... I was hoping to hear you had some sense of regret."

RELATED: Senate Democrats set to grill Mike Waltz over 'Signalgate' during confirmation hearing

Photographer: Kent Nishimura/Bloomberg via Getty Images

Senator Tim Kaine (D-Va.) also grilled Waltz over the alleged sharing of sensitive information on Signal. Waltz confirmed when pressed that “Signal has not been approved for use by U.S. government officials for the sharing of classified information."

Senator Kaine didn’t stop there. He pressed Waltz on the ongoing investigations surrounding the alleged Signal leak of classified information. Waltz responded: "I shouldn't and can't comment on an ongoing investigation, but what I can do is echo Secretary [Pete] Hegseth's testimony that no names, targets, locations, units, routes, sources, method … no classified information was shared."

Senator Cory Booker (D-N.J.) accused Waltz of avoiding responsibility, saying that it was not an acceptable excuse to say that Jeffrey Goldberg was "sucked in" to the message group.

Booker continued, "Instead, in a moment when our national security was clearly compromised, you denied, you deflected, then you demeaned and degraded those people who objectively told the truth and criticized your actions."

"It shows profound cowardice. ... Even after weeks, if not months, of reflection, you couldn't sit before this committee and take some responsibility."

Waltz faced pressure from his own party as well. Senator Rand Paul (R-Ky.) questioned Waltz on where his loyalties exactly lie: "I guess it just worries me that you come more from the Liz Cheney wing of the party than the Donald Trump wing of the party."

Waltz, a former U.S. representative from Florida, affirmed his loyalty to President Trump, citing his voting record in Congress: "Senator, I am squarely with the president. I've been with him in every single election I've participated in."

Mike Waltz needs a majority vote in the 53-47 Republican-controlled Senate to be confirmed as the new U.N. ambassador. A vote on his nomination is expected before the U.N. General Assembly opens on September 9.

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