How many times did U.S. President Barack Obama and his opponent, Mitt Romney, mention Japan in their three election debates this month? Zero. How many times did they utter the word China? 53.

The frequency of the mention of certain foreign nations in presidential debates is by no means the most accurate measure of the U.S. government’s diplomatic priorities. But it is often a good indicator of the levels of interest American voters are believed to have in each foreign affairs issue. For example, during the election debates...