Senators grilled Hegseth on Iran. Here are 3 big moments from the hearing

Hegseth said at the top of the hearing that the supplemental funding was an "urgent, necessary injection of resources" for the department's needs. He didn't directly mention the Iran war in his opening statement.

"We know the best way to create peace is to prepare for war, to deter it," said Hegseth. "That's exactly what the Department of War is doing: building a force so capable that it would be absurd for anyone to challenge it."

Given the latest escalation with Iran and the additional money being requested, Murray warned the U.S. could be sliding into "another forever war."

Late in the hearing, Sen. Gary Peters, D-Mich., said the Trump administration's efforts have been "an utter and complete failure to win this war."

"You, sir, are the failure," Peters retorted. "Not the men and women who are on that front line, not the men and women who hold up their honor with distinction," he added, raising his voice. "You don't have a long-term plan to actually win this war. Win the war!" Peters implored Hegseth.

The defense secretary responded by saying Peters has "Trump Derangement Syndrome," and accused Democrats of playing partisan politics and not funding the troops.