Lend-Lease was to circumvent American laws introduced following World War One; there was nothing in international law against it. Since it required the British to pick up what they were ‘leasing’ and ship it themselves initially it would not be affecting America’s Neutrality status; Hitler would have no justification for such an ultimatum. Expect a speech from Roosevelt stating that America’s actions will not be dictated by Berlin.
Is everyone sure that it would make no difference to Congressional votes?
I have to say that Lend Lease was a great and moral thing. I also have to say that it was NOT a neutral act and that any power in a state of war would have resented a third party doing this.
It would not have been strategically clever for Hitler to have declared war on the US in March 1941, but then it was not smart in December 1941 either.
This would depend if he gave reasons for it, and was clear on wheather it would result in an actual declaration of war or if it would just be treated as such and lead to an undeclared war.