WASHINGTON — Veterans of the wars in Iraq and Afghanistan now serving in Congress have emerged as some of the most important voices in the debate over whether to give President Obama a broad authorization for a military campaign against the Islamic State or something much more limiting.

In other conflicts, Congress shaped military policy with a certain remove from the battlefield. But as lawmakers deliberate whether to give authority for a military operation to a president for the first time since 2002, there are 26 veterans from the United States’ two most recent wars serving in the House and Senate, according to the group Iraq and Afghanistan Veterans of America. To them, this fight is not a distant foreign conflict. They have an intimate understanding of battling the same kinds of deadly extremists.

“One of the reasons I ran for Congress was to make sure we didn’t repeat the mistakes of the past, of going into war without a clear strategy,” said Representative Tulsi Gabbard, Democrat of Hawaii and an Iraq war veteran.

As a member of a National Guard medical unit who was responsible for reviewing the previous day’s casualty list, she said, she wondered whether “the leaders of our country and those in positions of making these decisions really understand what the impacts of their decisions were.”