Final answer:
Lindbergh and many Americans supported isolationism and neutrality as Hitler's Blitzkrieg continued in Europe; however, the US gradually shifted its policy from strict neutrality to supporting the Allies before eventually entering the war due to direct attacks.
Step-by-step explanation:
The policy that Lindbergh suggested America should adopt regarding the European war as Hitler's Blitzkrieg advanced was one of isolationism and neutrality. Lindbergh was a prominent figure who advocated against American intervention in World War II, believing that the United States should remain neutral and avoid becoming entangled in European conflicts. His views were reflective of a broader isolationist sentiment present in the United States during the 1930s and early 1940s, which influenced the policies of the Neutrality Acts passed by Congress.
As the Axis powers' aggression intensified, President Roosevelt gradually shifted away from strict neutrality, supporting the Allies through means such as the "cash and carry" provision to sell arms, while also enforcing economic sanctions against aggressor nations like Japan. Ultimately, despite the isolationist policies and public sentiment, the direct attacks on American vessels and Pearl Harbor forced the United States to enter the war.