WASHINGTON (TNND) — President Donald Trump's nominee for U.S. ambassador to the United Nations, Mike Waltz, is set to testify before lawmakers on Tuesday for the first time since he mistakenly added a journalist to a private Signal chat used to discuss sensitive details about a military strike in Yemen.

Secretary of State Marco Rubio took the position as national security adviser in May after Trump announced Waltz's nomination.

"From his time in uniform on the battlefield, in Congress, and, as my National Security Advisor, Mike Waltz has worked hard to put our Nation’s Interests first,” Trump wrote on Truth Social at the time.

The former Republican congressman's confirmation hearing will take place before the Senate Foreign Relations Committee at 10 a.m. and provide senators with the first opportunity to grill Waltz over revelations in March that he added The Atlantic editor-in-chief Jeffrey Goldberg to a private text chain.

The chat included several top officials, including Secretary of State Marco Rubio, Vice President JD Vance, and Defense Secretary Pete Hegseth.

In recent days, Waltz has been meeting with Democrats and Republicans on the Foreign Affairs Committee.

He only needs a majority in the 53-47 Senate, which Republicans control, to win.

Sen. Tammy Duckworth, D-Ill., said in a May interview with CBS News that Waltz would have a "brutal, brutal hearing," and described his nomination as "failing up."

"He's not qualified for the job, just by nature of the fact that he participated in this Signal chain," Duckworth said.

On the other side of the aisle, Sen. Lindsey Graham, R-S.C., said the Senate would "for sure" confirm Waltz.

"Some things I know for sure: the sun rises in the East, sets in the West and Mike Waltz will be confirmed as the next UN Ambassador," Graham wrote on X in May. "He is highly qualified, well-positioned, and will be a strong voice for our nation at the UN."

Previously, Trump nominated Rep. Elise Stefanik, R-N.Y., to represent the U.S. at the U.N. but pulled it in March, saying the House could not give up another Republican seat as the party clings to a razor-thin majority.

If confirmed, Waltz would be responsible for weighing in on resolutions, treaties and other global matters that affect the U.S.