While the public level of isloation was later, the attempts to set the narrative came before during the war (which remember had the backdrop of extremely poor Irish-American diplomatic relations , again I've never seen sources suggesting the US made active plans for attacking the Ports, by the time they had forces heavily deployed NI was fine for them. I find it hard to imagine that FDR would risk the potential blowback from the Irish American bloc that any active hostilities between the US and Ireland would risk?