Sen. Bernie Sanders (I-Vt.) at a rally in Oklahoma blasted President Trump’s decision to bomb Iran and enter the U.S. into Israel’s war with Tehran.

Sanders broke the news to the crowd in Tulsa, which began chants of “no more war.”

“I agree,” Sanders told the crowd. “Not only is this news that I’ve just heard alarming . . . but it is so grossly unconstitutional. All of you know, that the only entity that can take this country to war is the U.S. Congress. The president does not have the right.”

Only Congress has the power to declare war under the U.S. Constitution, though presidents in both parties have carried out military strikes on adversaries without prior approval from the legislative body.

Lawmakers in both parties have been unnerved in recent days by the saber-rattling over the possible U.S. entry to Israel’s bombing of Iran. Trump just days ago said he would be making a decision in the next two weeks about bombing Iran.

Sen. Tim Kaine (D-Va.) introduced a resolution Monday seeking to prevent the U.S. from getting involved in a military conflict with Iran without congressional approval.

The resolution reaffirms existing law, directing the president to end any use of the U.S. armed forces “for hostilities” against Iran “unless explicitly authorized by a declaration of war or specific authorization for use of military force against Iran.”

President Trump announced Saturday the United States had bombed three Iranian nuclear sites, including the Fordow site that is located in a mountainside.

“We have completed our very successful attack on the three Nuclear sites in Iran, including Fordow, Natanz, and Esfahan,” Trump posted on Truth Social.

It was not immediately clear how successful the attacks were in eliminating the nuclear sites.