Attributing the famous quote about Americans doing the right thing after exhausting all other alternatives to Winston Churchill is unproven, as leading quotation researchers and Churchill scholars have found no documentary evidence in his recorded speeches, writings, or private papers.
Winston Churchill made the statement that Americans always do the right thing after they have tried everything else.

"Americans will do the right thing, after all other possibilities are exhausted"
Source: richardlangworth.com
Key Evidence
Comprehensive searches of Winston Churchill's extensive speeches, writings, and private papers reveal no record of the quote.
Prominent Churchill scholars and quotation research organizations classify the attribution as unproven and apocryphal.
What the Evidence Shows
The popular saying that Americans will always do the right thing after exhausting all other options is widely attributed to Winston Churchill in political discourse and popular culture. However, extensive research by prominent Churchill scholars, including Richard Langworth and specialized researchers at Hillsdale College, has failed to uncover any primary documentation linking the phrase to Churchill.richardlangworth.comrichardlangworth.com"Americans will do the right thing, after all other possibilities are exhausted"While Langworth included a tentative, unproven reference to it in his book Churchill by Himself under "Characteristics of Americans" (dating it circa 1944), he and other historians have categorized it as lacking provenance—noting that...
Snopes and dedicated quotation researchers like the Quote Investigator have similarly tracked the saying and determined it is apocryphal. While Churchill spoke and wrote extensively throughout his long public life, no reliable audio, transcript, manuscript, or published work contains this specific remark. Researchers note that alternative attributions have occasionally pointed elsewhere, such as to Israeli diplomat Abba Eban, but definitive proof remains absent.snopes.comsnopes.comWinston Churchill Americans QuoteRichard M. Langworth, a prominent Churchill scholar and the author of Churchill by Himself (the definitive compendium of Churchill quotations), has repeatedly searched through the millions of words written, spoken, and recorded by...
winstonchurchill.hillsdale.eduwinstonchurchill.hillsdale.eduAmericans Will Always Right ThingWhile Churchill famously held complex, often affectionate yet critical views of the United States (partially owing to his American mother) While scholars note that the sentiment aligns with private frustrations Churchill occasionally...+1 more