It's December 7 already

[MajGenl.Meade]

the fact that the United States had not intervened in Europe, but instead watched Britain get battered for some 26 months from September 1939 to December 1941, suggested to many in the Japanese military command that the United States might either negotiate or respond only halfheartedly after Pearl Harbor,[/b] especially after the envisioned loss of the American carrier fleet.

Not a very convincing source. The populist calls for isolationist policy, along with the Neutrality Act, may have fooled the Japanese (and the writer quoted above), but it's not a fact that the USA "watched Britain get battered for some 26 months until December 1941" as if it did not intervene.

Roosevelt got around isolationism re Europe with the Lend-Lease Act, among other actions, which cancelled the "cash and carry" policy of the stand-aloners and enabled Britain and the Allies to get "stuff-for-free-(for a while)" but which did not apply to the Axis powers. The Old Destroyer policy may seem a bit "old" but those ships were a god-send.

It was clear to the entire world (except Japan and US public opinion perhaps) that isolationism was not workable and was, in real-politik, evaded. Roosevelt et al were very much interfering in European affairs, risking war, and even more so in Asia-Pacific, risking more war. Which they got and which shut the mouth of the isolation mob very effectively. Well done, Japan!

Yes, the Japanese miscalculated - in effect, they were too patient and left their strike until too late. Hands-off policies in the USA had indeed led to low levels of preparedness for a real war - that's true. But in the very real sense, it wasn't isolationism that drove Japan to war but committed interventionism by Roosevelt, who got that for which he was looking.

But sure, isolationist rhetoric had its effect. Just not as much as US provocation.

[rubato]

Because of George C. Marshall the size of the US army was increased by ten-fold when we entered the war in 1942. Marshall knew that war was inevitable and that preparation was necessary and he convinced Roosevelt of it even though there was serious political resistance from the GOP (who were more afraid of paying taxes to build an army than they were of the Axis.)

And isolatonism was not the policy of the US government although Roosevelt was sensitive to the popular sentiments. Part of his greatness as president was his ability to sense how far he could go in the direction he knew was necessary in spite of popular resistance.

In August 1941, U.S. president Franklin Roosevelt and British prime minister Winston Churchill met aboard a cruiser anchored off Newfoundland to craft a proclamation that became known as The Atlantic Charter. In it, they vowed not to pursue gains, "territorial or otherwise;" to honor the right of every country to determine its own form of government; to ensure freedom of the seas; and to carry on peaceful global trade. Following a Roosevelt speech on January 6, 1941, Congress passed the Lend-Lease Act, which allowed the American government to supply war matériel to any country at war with the Axis powers. Britain became the main recipient.

yrs,
rubato