Using unrestricted submarine warfare by the Germans can trigger a few % towards joining, the same can trigger the Lusitania event, giving a large % towards joining (~15%-20%.)
Entente blockade of Germany can trigger a few % against joining (much rarer than the previous one)
DOW-ing in any country will shift against that side everyone, including the USA by a few %
In the Triple Alliance variant, the USA get regular events shifting towards joining, so it can happen much sooner
Around the Historical entry, it gets some massive shifting (AFAIK)
Mostly if you avoid the sub warfare as Germany, the US will not enter before IRL, and even than not sure, if you totally avoid it.
Just completed first CP game (SP) and US didn't enter until very late. Was a non-event really unlike SC-WaW and WiE where it's critical for Allies.