[3] Although he considered himself a socialist, Nishio was also strongly nationalist and virulently anti-communist, and was fond of saying that he came to socialism not via Marxism but rather through “idealistic humanism” (risōteki hyūmanizumu).

[4] In 1942, Nisho was reelected to the Diet despite being a "non-recommended candidate," meaning he had not received a recommendation from the single national political party, the Imperial Rule Assistance Association.

Unlike many other Socialist leaders, Nishio maintained strong connections with big business interests, which facilitated his rise within the party.

When the left and right Socialists re-merged in 1955, in a shotgun wedding as a response to the threat presented by the unification of Japan's conservative parties into the Liberal Democratic Party (LDP), Nishio vocally opposed the merger, fearing that the left Socialists were fellow travelers with communists, and was brought over only with great difficulty by appealing to the need for solidarity against the conservative threat.

Although the Japan Socialist Party and Sōhyō took leading roles in the protest movement and vowed to stop the passage of revised treaty, which they viewed as cementing in place the U.S.-Japan military alliance in the service of Japanese monopoly capitalism, Nishio remained a Japanese nationalist who favored the revised treaty as a better deal for Japan.

[3] The left wing of the Socialist Party and the leaders of the Sōhyō labor federation decided that Nishio was impeding the anti-treaty struggle and began taking steps to have him booted from the JSP.

[10] Although the DSP managed to cling to a few seats in the Diet for a few more decades, it was never able to recapture the excitement it had accrued at the time of its formation, especially after the conservative LDP became more moderate under prime ministers Ikeda Hayato and Eisaku Satō.