Seriously, if the US did stay on the sidelines for the war in Europe, could the UK have enough military capacity to prevail over the Nazi's?
I say its a resounding NO!!!
While the UK did have the power to not be invaded by the Germans, it also flat out didnt have the power to invade France or Italy.
Only the US had the resources necessary to enable the allies to beat the Germans. In fact, without the US getting involved in the European war, the Germans would have fought the Russians to a draw, or maybe even with some luck, beat them.
The facts are clear, the US saved Europe from Russian or German domination