Biden, who didn't mention Russian President Vladimir Putin or Trump by name, likened the war in Ukraine to WWII during remarks at an American cemetary in Colleville-sur-Mer for the 80th anniversary of the D-Day landings in Normandy.

"We're living in a time when democracy is more at risk across the world than any point since the end of World War II," read Biden during the Thursday speech.

"Isolationism was not the answer 80 years ago and is not the answer today," he continued, defending the role of NATO as essential to preserving freedom. "To surrender to bullies, to bow down to dictators, is simply unthinkable. Were we to do that, it means we would be forgetting what happened here on these hallowed beaches. Make no mistake: we will not bow down, we will not forget."