I've always viewed that as Joseph Kennedy following the Nazi party line, and backing off from it after FDR chewed him out. MI5 and the FBI raised concerns about him after he hired a Nazi spy named Tyler Kent to his staff in late 1939. In December 1940 the FBI reported to FDR that Kennedy was involved in negotiating a peace between Germany and Nazi sympathizers in France, prompting FDR to hold a cabinet meeting about what to do with Kennedy. A bit after that Kennedy made a public statement attacking Lend-Lease. That was the last straw for FDR, and he called Kennedy in and personally laid into him. I believe Kennedy's shift in party line started after that incident.
Sorry about the double-post; my server's not connecting well this afternoon.
Thanks. You know a lot more about this than I do. Mostly I'm going from old memories and things read a long time ago.