In your opinion, how would major events in American history like the Civil War, the Great Depression, both world wars, superpower status, the Cold War, etc be handled if the founding fathers imposed a British-style form of government? This means shaky Coalition governments, which in turn leads to a fundamentally weaker Prime Minister and cabinet than in a presidential system, including the possibility of instant removal with the loss of a majority in Parliament rather than the set term. A huge effect will be the fact that the Prime Minister is not supreme commander of the armed forces.
Name any worthwhile event in American history, and describe how you think it would be handled with a parliamentary government. Make it after 1787, when the need for a constitution was agreed upon (the USA was run by the Articles of Confederation before then).