Mitt Romney unavailable for comment.

WASHINGTON, July 8 (Reuters) – Russia is the biggest threat to U.S. national security and America must boost its military presence throughout Europe even as NATO allies face budget challenges and scale back spending, U.S. Air Force Secretary Deborah James said on Wednesday.

“I do consider Russia to be the biggest threat,” James told Reuters in an interview after a series of visits and meetings with U.S. allies across Europe, including Poland.

James said Washington was responding to Russia’s recent “worrisome” actions by boosting its presence across Europe, and would continue rotational assignments of F-16 fighter squadrons.