I think when a president makes a dumb mistake, people’s reactions depend not only on the president but on the type of mistake and the context. When George Bush Sr., in an address to American Legion members, referred to September 7th as Pearl Harbor Day, it didn’t elicit much of a reaction, because he was a World War II veteran. But when Dan Quayle misspelled “potato” as “potatoe”, everyone made fun of him, because he already had a reputation as someone who was inexperienced.
Obviously Obama got this wrong though. America invented mass production of the automobile, but not the automobile itself.