Why did having soviet union as an ally contradict one of the reason for us involvement in the war?

Having the Soviet Union as an ally contradict one of the reason for the US involvement in the war as this is because of the fact that they are likely inadvertently going to war to each other and that they are likely to be doing this in Korea.

richard milhous nixon (january 9, 1913 – april 22, 1994) was the 37th president of the united states, serving from 1969 to 1974, when he became the only president to resign (quit). he is also known for corruption and the watergate scandal which resulted in the public losing trust in him and his resignation.