How does the popularity of a president’s policies impact his or her party’s electoral chances? Why have Latinos — and other voters of color — swung toward the Republican Party in recent years? How does the state of the economy influence how people vote, and which economic metrics in particular matter most? We can’t answer those questions yet for 2022. But we can look at previous elections for insights into how things could play out. John Sides and Lynn Vavreck — political scientists at Vanderbilt and U.C.L.A., respectively — have routinely written some of the most comprehensive analyses of American presidential contests. Their new book, “The Bitter End: The 2020 Presidential Campaign and the Challenge to American Democracy” — written with Chris Tausanovitch — is no exception. The book’s findings are built on top of numerous layers of data and analysis, including a massive survey project that involved interviewing around 500,000 Americans between July 2019 and January 2021. We discuss the core questions of 2020: How did Donald Trump come so close to winning? Why did Latinos swing toward Republicans? What role did Black Lives Matter protests have on the outcome? How did the strange Covid economy of 2020 affect the election results? And of course, what does all of this portend for the midterm elections in November?