What Progressive political reforms changed the political influence of immigrants?

There were two significant factors in Progressive politics and ideology that led to a decline in immigration and a decline in the influence of immigrants.

The first of the two is one likely to be repugnant to many people of the twenty-first century. Due to their interest in science and the potential of science and technology to improve the world, many of the Progressives embraced eugenics, arguing that just as we can breed horses to...

There were two significant factors in Progressive politics and ideology that led to a decline in immigration and a decline in the influence of immigrants.

The first of the two is one likely to be repugnant to many people of the twenty-first century. Due to their interest in science and the potential of science and technology to improve the world, many of the Progressives embraced eugenics, arguing that just as we can breed horses to improve racing performance or cattle to improve meat production, so selective breeding can improve the human race. This effort had two prongs. The first was attempts, especially on the state level, to sterilize people deemed unfit to breed, especially the mentally disabled. The second was an effort to restrict immigration, especially by people from "inferior" races. This attitude that certain races were by nature inferior led to negative attitudes towards immigrants, restrictions on immigration, and reduction of immigrant influence. 

The second anti-immigration aspect of the Progressive movement resulted from its strong connections with labor movements and unions. Many unions were opposed to immigration because they believed that an influx of unskilled Asians willing to work for extremely low wages would depress salaries and reduce the negotiating power of unions to improve working conditions. The unions allied politically with Prohibitionists who thought that immigrants from certain countries brought with them a culture of drinking that contributed to immorality. Religious prejudices of a Protestant majority against Jews and Catholics played into this anti-immigrant sentiment. One resulting policy was that of Americanization, in which the public school system was used to instill American values and fluency in English into the children of immigrants. This policy of assimilation reduced the influence of immigrants by causing younger generations to assimilate and to consider themselves primarily as "Americans" rather than as members of an immigrant community.