As the historian, how do you assess the credibility of the two accounts?

The first key points historians want to check about a source is whether the source is based on accurate knowledge and understanding. To do this, they might check whether the author was there at the time, whether the author was involved in the event, whether the author understood the overall context.

The United States of America joined World War II when Pearl Harbor was bombed...if you're referring to the 2nd World War.