Please notice that the authors use different sources to substantiate their claims and justify their research. When the authors say, "politics today ... is especially divided along ideological lines" (Sterling, Jost, and Hardin 2019; para. 2), it is a claim (an argument). However, when the authors cite all the sources they cited, it is their way of saying, all these people agree with us. Then, it becomes a substantiated claim -- a claim with support (intellectual and empirical support).
That is why science, including social science, is a team sport. It is a bit more like a contact sport like football, and one'd better be ready for a big tackle when making any scientific claims. Scientists challenge each other's theory, research methods, and findings all the time, keeping each other humble and in check. For this very reason, scientific knowledge takes a long time to develop, emerge, and be accepted as knowledge. For this very reason, scientific knowledge is more credible and reliable, too.
Read the following sections, titled "A Few Illustrative Examples" and "Social Psychological Theory..." Identify a section where the authors did a good job using other research to illustrate, describe, explain, and/or substantiate their claims. Briefly tell us why you like it.