It's really curious that some people here seem to think that German submarine warfare resulting in loss of American lives was limited to the Lusitania--at least that's the only incident they ever mention. They seem to have forgotten about the Falaba (the "Thrasher incident"), the Gulflight, the Ancona, the Arabic, the Sussex... My point is not to debate the facts of these incidents one by one but to emphasize that it was the cumulative effect of all these incidents that left a very bad impression of Germany in the American mind. Now, Americans for the most part did not want to go with Germany over these incidents, and were generally happy when the Sussex pledge seemed to put an end to the immediate threat of such a war. Once that was done, they did devote more attention to British violations of American rights, and undoubtedly any were upset about them. But not so upset that they wanted to go to war with the Entente, let alone to align themselves with a Germany that had perpetrated all these incidents (as well as espionage and sabotage in the US). The Entente, like the Germans, could violate American rights to some extent without the US going to war.
It's too late, they're already talking about the US, after losing a ship, invading long time friend and ally, Canada :/