What political evidence supports the argument that the US should not have entered WWI?
America should not have entered WWI for many reasons. Germany had a right to blockade Britain as Britain had mined the North Sea. Furthermore, Britain flew the flags of neutral vessels to avoid attack, which broke laws of maritime warfare at the time. For America to claim neutrality when it sold arms and made loans to Allied nations was questionable at best.
America also claimed to be influenced by German atrocities at the Western Front, especially against Belgium. These atrocities were largely overblown by the British and French media, and even American servicemen and news correspondents who went to the Front said that they did not see any war crimes committed against the Belgians. Early in the war, Britain cut the German transatlantic ocean cable, ensuring only the Allied side of events went through.
Also, look at Wilson's rationale for going to war--"a war to make the world safe for democracy." America backed two imperial powers in Britain and France who had long treated their colonies in Africa and Asia poorly, and we lent aid to the autocrat czar Nicholas II. This was not a war of good vs. evil--it was a European squabble that threatened to destabilize the balance of power in Europe.