You could read a biography of Bryan; he was an important figure of the era, so there's plenty to choose from.

A great short biographical sketch can be found in Richard Hofstadter's classic The American Political Tradition and the Men Who Made It (https://www.goodreads.com/book/show/773961.The_American_Poli...), which is an excellent, compulsively readable book, though Hofstadter had a low opinion of Bryan so this is not the source to turn to if you want to argue with me. The "I will look up the arguments later" quote can be found in Robert Cherney's A Righteous Cause: The Life of William Jennings Bryan (https://www.goodreads.com/book/show/1704339.A_Righteous_Caus...), which I haven't read myself but looks to be a good general-interest book-length biography. A contrarian view on Bryan can be found in Michael Kazin's A Godly Hero: The Life of William Jennings Bryan (https://www.goodreads.com/book/show/79196.A_Godly_Hero), but the rehabilitation of populism has been a project of Kazin's for decades now, so it will come as no surprise that Kazin has more respect for Bryan than most historians.

Research? "The people of Nebraska..." quote is quite famous.