If the fallout could be limited to JUST the United States I'd wish for a Trump victory in a heartbeat - no nation needs to be brought to its knees quite like the United States of America.Trump will end democracy in the USA. It will be brutal and will split the country forever.
Realistically though, the dissolution of the United States into factional enclaves, some conservative, racist and outright evil while others liberal, left and inclusive will have massive financial repercussions for the rest of the world.
The United States has wormed and thieved and connived and bribed and sweet-talked and bought its way to be the world's indispensable nation, at the financial and cultural heart of most of everything. Its fall won't be the flutter of a butterfly's wings that creates a simple storm on the other side of the world.
As the bald eagle dies, the last convulsive flap of wing could spawn nightmares.