How did WWI affect political life in the United States?Also, what techniques were used to stifle dissent?
The largest impact of the First World War on political discourse in America was its treatment of those who dissented. The Espionage Act which was passed almost immediately after the United States entered the war allowed the government broader freedoms to stifle dissent, imprison those whose speech was deemed to interfere with the operations of the military, and enabled citizens to become more active agents in identifying where potential treasonous behavior might lie. Activists like members of the worker's union, the IWW, and Eugene Debs were imprisoned for their beliefs and the articulation of them. The desire of the government to present a completely coherent front in its attempt to "make the world safe for democracy" had an adverse effect in trying to repress the same democratic tendencies on a domestic front.
The Supreme Court sided with the government in Schenck vs. United States, ruling the Espionage Act constitutional and limits on free speech by the government constitutional as well. They wrote that, when there was a "clear and present danger" to the national security of the United States, it was OK for the government to limit civil liberties. This ruling was used as a precedent for Korematsu vs. US during World War II, and Dennis vs. US during the Cold War.
Since Schenck was also a socialist leader at that time, he along with Debs were essentially targeted by the government. As the Russian Revolution took place in 1917, the anti-communist sentiment in the American people and government rose as well.
World War I tended to stifle political life in the United States. This was especially true of any sort of political life that would tend to hurt the war effort. There was not an election while the US was at war, so we do not know how that would have played out, but we do know that dissent was stifled.
The main way that this was done was through the Espionage Act of 1917. This law made it illegal, more or less, to do anything that the government said would hurt the war effort. That is why Eugene Debs was jailed for speaking out against the draft.
There was also mob violence against people who were against the war. Finally, the government also prevented various anti-war activists from sending mail.