Would the US have fought Germany if Germany (and Italy) had not signed a pact with Japan?

Japan attacked the US and the US smoked them. The US also fought Germany and Italy because of the Treaties with Japan. Given the isolationist mood of the US during the 1940's would the US have opened a second front (Atlantic) if there was no treaty? Remember, the US did not (and I'm asking would they have) come to Britain's aid until the attack on Pearl Harbor.