"We have about 20 years of a different paradigm to correct," Gen. Philip Breedlove, commander of U.S. European Command, said during testimony before the House Armed Services Committee, the report says.

Breedlove, who has led EUCOM during the command’s biggest transformation in a generation, said he did not foresee a need to return to a Cold War-style military posture. But the era of trying to make a partner of Russia is over, and key U.S. capability gaps need to be addressed, he said.

"Russia has chosen to be an adversary and poses a long-term existential threat to the United States," Breedlove said.

"This is not the Cold War, but I do believe we are not where we need to be now in a mixture of permanently forward-stationed forces and pre-positioned stocks so that we can rapidly fall in on it," Breedlove said.

NATO is now reviewing a plan to increase its presence along the eastern flank with a new multinational unit. But to deal with Russia in a military confrontation, allies would need to be able to break through Kaliningrad, a Russian enclave nestled between Poland and Lithuania on the Baltic Sea — what Breedlove described as a "fortress" filled with weapons systems that can target allies from land, sea and air.

"We need to make sure we have the capacity to… break it so that we can continue to rapidly reinforce," Breedlove said.