A second Republican senator has joined bipartisan voices in defending NATO, pushing back against President Donald Trump’s suggestion that the United States could withdraw from the alliance.

Senators Thom Tillis and Jeanne Shaheen, who co-chair the Senate NATO observer group, emphasized the alliance’s historic support for the U.S., particularly after the September 11 attacks.

They warned that any move to exit NATO would weaken American national security and align with the strategic interests of global rivals such as Vladimir Putin and Xi Jinping.

Their remarks followed similar criticism from Senate leaders, including Mitch McConnell and Chris Coons, who highlighted NATO’s role in supporting U.S. military operations in Afghanistan and Iraq.

Trump, a longtime critic of the alliance, has recently intensified his rhetoric, saying he is seriously considering withdrawing after NATO declined to participate in joint military operations involving Israel and Iran. He has also questioned the alliance’s value and signaled that withdrawal remains under active consideration.

Despite the president’s comments, leaving NATO would face significant legal and political hurdles. A 2024 law requires either a two-thirds vote in the Senate or an act of Congress for the U.S. to formally exit the alliance.

The dispute has exposed a rare divide within Republican ranks, with some lawmakers—particularly those nearing the end of their terms—publicly challenging Trump’s stance on one of the cornerstone alliances of U.S. foreign policy.