Answer:
D. Most politicians who supported the cause of the Irish immigrants were Democrats
Step-by-step explanation:
Even though, President Harry S. Truman is a democrat. The passage did not imply that "Most politicians who supported the cause of the Irish immigrants were Democrats."
Because the passage only made mention of the name of the President that once attended the St Patrick's Day parade in New York. And also there other political candidates who attended the Day but not that majority of the Democrats politicians support the cause of the Irish.