"That you're not only outlining the timeline — which is troubling, but you're also talking about specifically how many troops, how many brigades, where they're coming from, and what they're going to be doing," she added.

Military officials at the briefing said the offensive was planned for around April or May and would take around 20,000 to 25,000 troops, and described how Iraqi forces planned to approach the city, which ISIS seized in June.

Pentagon officials said Monday that the briefing did not reveal anything that wasn't spoken about publicly before or that was sensitive, but Gabbard said "it was no excuse."

She also said the White House needed to shift its strategy against ISIS but did not elaborate. "We need to shift our strategy, so I'm going to keep working on it," she said. "We have to stop them in their tracks and defeat them militarily and ideologically." The Hawaii Democrat has been at odds with the administration over its strategy against ISIS, calling for the administration to arm Kurdish forces directly and acknowledge that the war is against Islamic extremists.

"The reason why I feel so strongly about this is personally, is because it comes from my own experience at having served in Iraq," she said. "I served in a medical unit, where I saw the cost of war every single day and understand the need to make sure we don’t make the same mistakes again," she said.

"This is an issue that transcends partisan politics," she said. "It's something that we need to have a vigorous debate and dialogue on."