(no orders have yet to be placed in the US because Vickers can still deliver tanks and Böhler can still deliver antitank guns). So the NEI are not (yet) relying on the US for equipment
More important is the US did not dial down the Neutrality Acts until after Europe went to war in 1939. With the Neutrality Acts intact Arms exports and war material from the US is not happening. No mass of European orders to jumpstart US aircraft industry into the war plane business. Maybe they can get DC-3 or Venturas to apply 'bomber kits' to but even that is problematic the way the Neutrality Acts were intended.
This leads back to the "political Effect" referred to in the OP. For the US the European War both galvanized the Isolationist movement, and undercut it. Without the inflammation of a war neither the Isolationis not Warhawks have as much fuel for their view. Without war disrupting the US/European trade the problems of the isolationist position are forced to the surface and the Warhawks don't have a major talking point.
The question of the 1940 campaign has already been raised. I agree its unlikely Roosevelt will run, & its possible the next president is Republican with a Republican legislature. This does not automatically mean a isolationist administration. The Warhawks were as likely to be a conservative Republican as Democrat and leftists or the merely left leaning were strong Isolationist supporters circa 1940. That many of the isolationists were actually anti Roosevelt is a factor as well. The course of US attitudes towards European tensions, continued rearmament, and general political climate can vary in unpredictable ways absent a war & who takes up the leadership in Congress and the Executive.
I'd make a guess this applies to Britain as well. The anti war feelings there cannot be easily dismissed, & neither can the fiscal conservatives who dislike military spending. Were the Polish crisis to pass without war there is a possibility any likely government would dial down support for France and rearmament to some small or greater degree.
France has the deep running motivation of denying Germany any major influence politically or economically. While that is in the long a run a losing battle it still informed Conservative and centrist thinking. Unless there is some sort of massive Volte-Face in German policy and action France is going to continue its rearmament and political containment policies, however unsuccessfull.
Italy Im unsure of, knowing even less of its internal politics or Mussolinis thinking.
Germany is the wild card. If there is not further diplomatic or military success then the nazi regime is still vulnerable to a military coup. Perhaps Hitler will overreach in some decision or other & trigger that. The question then is if the new regime dials down the deficit spending, armaments programs, and seeks a stable foreign policy. If the nazis remain in power do they pursue better spending policies, or double down on fiscal smoke & mirrors and fraud?