During research for an essay, when should you write down information about the source and its location

Which passage from kennedy's inaugural address is an example of an allusion? to our sister republics south of our border, we offer a special pledge-to convert our good words into good deeds-ir new alliance for progress but this peaceful revolution of hope cannot become the prey of hostile powers a call to bear the burden of a long twilight struggle, year in and year out, rejpicing in hope patent in tribulation it a free society cannot the many who are poor, it cannot save the few who are rich