1. Agiesta, Jennifer. 2019. Iowa Poll: Trump Remains Strong Among Iowa Republicans, But Some Hope for a Challenger. CNN, March 11.
https://www.cnn.com/2019/03/11/politics/cnn-poll-iowa-republicans-trump/index.html
.
2. Ansolabehere, Stephen, and Brian F. Schaffner. 2017. Cooperative Congressional Election Study, 2016: Common Content. [Computer File] Release 2: August 4, 2017. Cambridge, MA: Harvard University [producer].
http://cces.gov.harvard.edu
.
3. Bitecofer, Rachel, and Quentin Kidd. 2019. National Survey of 2020 Likely Voters. The Judy Ford Wason Center for Public Policy, Christopher Newport University, February 26.
http://wasoncenter.cnu.edu/wp-content/uploads/2019/04/Wason-Center-2020-National-Survey-Report-Final.pdf
.
4. Breuninger, Kevin, and John W. Schoen. 2019. Here’s What the 2020 Democratic Candidates Say They’ve Raised in the First Quarter. CNBC, April 3.
https://www.cnbc.com/2019/04/03/heres-what-the-2020-democratic-candidates-raised-in-the-first-quarter.html
.
5. Cohen, Marshall, and Jeff Simon. 2016. How Democrats Lost Dubuque, and Middle America. CNNPolitics, December 14.
https://www.cnn.com/2016/12/14/politics/democrats-lost-dubuque-middle-america/index.html
.