But, until Pearl Harbor and the Philippines there was no clear pretext for the US to declare war. And had they not attacked, it's not clear that FDR could have gotten congress to declare war. Some of those prominent supporters were significant industrialists like Ford, they would have fought intervention by all means.
After Pearl Harbor, there was no debate.
Maybe the first and third were seen as necessary to protect a neutral country? Or being short of declaring war, they were less objectionable? But I'm just guessing ...
Lend-Lease had fairly staunch resistance, as it basically shredded any pretense of neutrality. The draft and the military build-up were supported in large part due to neutrality--the need to have a sufficiently strong military to deter potential aggression (this was the strategy of Switzerland). When FDR extended the draft term from 12 months to 18 months, it passed by a single vote in the House.
But, yes the US had a constant stream of arms being supplied to Britain and Russia during the period before the war.
That seems like conventional wisdom, but the U.S. started a large military build-up before Pearl Harbor. The military draft began in 1940. And of course the U.S. was actively supporting the UK through lend-lease.
There were still isolationists in Washington and even prominent supporters of Hitler in the public sphere (if you ever wonder how misguided people can be, remember that), but certainly there were many indications that the U.S. would enter the war.