Well didn't the Americans not go to war during WWI and refused to, but only did because of Lusitania?
There were a range of factors prompting US intervention. Other sinkings of civilian ships and US deaths, the Zimmerman telegraph, general militaristic behaviour of imperial Germany, allied debts to the US.
I have another question: would the Isolationist America have less power in world politics, and be less powerful in general?
Especially if anything like Japanese isolation it would have a lot less power and be a lot smaller. For one thing it would reject further annexations or other territorial gains, since that would mean interacting with other nations and taking on new people. For another it would not welcome immigrants so a lot less people and knowledge. Ditto for greatly reduced foreign trade.
If a deeper and longer lasting American isolationism then probably no war with Spain and annexation of the Philippines. Less contact with the outside world and hence less influence. Smaller forces, especially naval until the policy changes. America, presuming still successful economically would continue to be a sleeping giant, largely overlooked by the rest of the world because it doesn't interact with them much.
Steve