The NEA stopped its meeting to prevent the American Legion from defending itself against the "fascist" allegation.
The convention was to hear from FDR the next day and maybe the cutoff was a way of keeping Doherty off the platform until then. They apparently were going to move to the World's Fair site for FDR's speech the next day and could offer the excuse the President was a more important speaker than Doherty. Maybe Doherty would be allowed to speak before an empty or semi-empty hall instead of the large evening crowd.
Some background though is in order on FDR and 1938 politics here. Roosevelt was blocked in his New Deal initiatives by conservative Democrats and he devoted major energy to taking them out in 1938 Congressional elections. He actively campaigned to replace them with New Dealers (imagine a Republican president taking out liberals in the GOP primaries).
Groups like the National Education Association and the Congress of Industrial Organizations (CIO) were all involved in supporting the Roosevelt agenda of liberalizing the Democrat party in 1938 primary elections.
FDR the only President that ruled for life.
He ignored the two term tradition and ruled until his death.
"Groups like the National Education Association and the Congress of Industrial Organizations (CIO) were all involved in supporting the Roosevelt agenda of liberalizing the Democrat party in 1938 primary elections."
Have you read "Hollywood Party?" Lots of good stuff in there about commies in the unions.
With groups like the Friekorps kicking commie ass in Germany the NEA had a well grounded fear of politically active ex-military.