I believe Woodrow Wilson was the worst president this country has ever seen. Under his administration he segregated federal employees, personally vetoed a clause in the League of Nations charter calling for racial equality and had more race riots under his administration than any other president.

http://www.pressroom.com/~afrimale/wilson.htm
http://www.jiyuu-shikan.org/e/db1b.html
http://www.jimcrowhistory.org/resour...race_riots.pdf

In 1918 American troops were sent to Russia under the pretense of reopening the Eastern Front but they spent their time fighting Bolsheviks instead. They remained until June of 1919, long after the end of World War I. This incident, in my opinion, laid the framework for the Cold War.

http://www.umich.edu/~bhl/bhl/mhchome/polarb.htm

After the United States entered World War I it became illegal to speak out against the war under the Espionage Act. People were arrested and imprisoned for their opinions.

http://www.spartacus.schoolnet.co.uk/FWWespionage.htm