The Congress was dominated by an alliance of Socialists, Anarchists, Communists and Syndicalists (and smaller left groups), but the majority of the left (along with the Republican-Democrat Pact, which was the remaining opposition) wanted neutrality in the war. However, on one side, Ruthenburg wanted the USA to join the war, so he (illegaly and secretly) manufactured the Toronto Accident to have a pretext. Which would lead to his impeachment (which was applauded by both left and right) and the USA exiting the war with a negociated peace (with only military limitations and reparations).
On the other hand, even if Ruthenburg deserves the hatred, it was not only his fault that the USA entered the war. The Alliance of the Five Empires provoked the USA a lot. The Kriegsmarine, Royal Navy and IJN practiced unrestricted maritime warfare (both surface and submarine) against the US trade with the French Socialist Federation (for example, they sank the Saratoga when it was going to the French port of Dakar), the Mediterannean Socialist Union (American civilian ships were sank or confiscated illegally, with their crews molested, when they were going to Athens, Naples, Lisboa and Barcelona), the Siberian Commune, Persia and the Imperial Republic of China.
It was somehow inevitable, as in the pre-war years, the USA had focused their trade with the Socintern countries.
Then, there was the problem of the British-German occupation of Iceland and Greenland, as well as the British-German intervention (in 1934) to crush the revolution in Venezuela, which directly flew in the face of Monroe Doctrine.
However, despite all those provocations, if Ruthenberg hadn't manufactured the Toronto Incident (three months after the Saratoga), the USA wouldn't have joined the war. After the Saratoga Incident, the Congress accepted to deliver lend-lease to the Socintern (with armored convoys) as well as threaten the Five Empires with war if they again intervened in Latin America, but still, the Congress hadn't actually wanted to join the war. Until Ruthenberg forced their hand.