Isolationism caused WWII

In between the two world wars, America went isolationist.  We came to believe that the first world war was a big mistake, we should never have entered it, and we should never again get sucked into a European war.  America withdrew from Europe. 

    And then Hitler came on the scene.  He gained control of Germany in 1932, and by 1936 he felt strong enough to start causing trouble in the international scene.  All of Europe, even including Germany, was still in shell shock from World War I.  Both the British and the French feared to oppose Hitler in the early days when he could have been deposed fairly easily.  Without Hitler, Germany might have thrown her weight around for a few years, but she would not have started WWII.  Nobody in Europe wanted to go thru another world war, they had had enough of that in the First World War. 

   If France and Britain had at the very first, the Rhineland takeover in 1932, mobilized their armies, and marched into Germany, they could have easily defeated the 100,000 man army which was all the Versailles Treaty allowed Germany, occupied the country, deposed Hitler and put him on trial for crimes against humanity.  But, neither the French nor the Britons did anything, partly thru fear of kicking off another world war, partly from fear that they would loose, and partly from domestic political problems.  If, America,  by this time a Great Power, had told the British and the French that the US was 1000% behind them, and had dispatched troops to Europe, a division or two would have made the point,  and had stood forth in the League of Nations and  condemned German violation of the Versailles Treaty, then something might have been possible. 

   Well, that didn't happen.  American isolationists forced the US to put on the turtle act, don't move, retract head and feet into shell, and do nothing.  With no US backing, the British and the French lacked the stones to take on Hitler when they could have beaten him with ease. 

     We can see and hear isolationists coming back to life today.  Last time they caused a world wide catastrophe.  What can they do this time?