Northwestern has roughly 225,000 alumni in all branches of business, government, law, science, education, medicine, media, and the performing arts. Among Northwestern's more notable alumni are U.S. Senator and presidential candidate George McGovern, Nobel Prize–winning economist George J. Stigler, Nobel Prize–winning novelist Saul Bellow, Pulitzer Prize–winning composer and diarist Ned Rorem, the much-decorated composer Howard Hanson, Deputy Prime Minister of Turkey Ali Babacan, the historian and novelist Wilma Dykeman, and the founder of the presidential prayer breakfast Abraham Vereide. U.S. Supreme Court Associate Justice John Paul Stevens, Supreme Court Justice and Ambassador to the United Nations Arthur Joseph Goldberg, and Governor of Illinois and Democratic presidential candidate Adlai Stevenson are among the graduates of the Northwestern School of Law. Many Northwestern alumni play or have played important roles in Chicago and Illinois, such as former Illinois governor and convicted felon Rod Blagojevich, Chicago Bulls and Chicago White Sox owner Jerry Reinsdorf, and theater director Mary Zimmerman. Northwestern alumnus David J. Skorton currently serves as president of Cornell University. Rahm Emanuel, the mayor of Chicago and former White House Chief of Staff, earned a Masters in Speech and Communication in 1985.

Which of Northwestern's alumni is notable for becoming a U.S. Senator and presidential candidate?