Nate thinks that Republicans and Democrats almost never work together in Congress.

. The reason he believes this is that he finds it much easier to think of examples of politicians from the two parties not working together than to think of examples of them working together. It is likely that the has caused Nate to underestimate how frequently Democrats and Republicans work together.
a. availability heuristic
b. confirmation bias
c. fairness bias
d. framing effect

a. availability heuristic

Explanation:

In psychology, the term availability heuristic, or availability bias refers to a cognitive bias where the person makes a judgement based on the immediate examples that come to his/her mind in a given moment. In other words, the judgement is based on what comes easily to the person's mind when thinking about a topic.

In this example, Nate thinks that Republicans and Democrats almost never work together in Congress (judgement), he thinks this way because when he thinks about it he finds easier to think of examples of politicians from the two parties not working together, in other words, he is making a judgement based on what comes easily to his mind (examples of politicians not working together).

Therefore, it is likely that the Availability heuristic has caused Nate to underestimate how frequently Democrats and Republicans work together.