Final answer:
Challengers generally lose in congressional elections due to the incumbency advantage, which includes factors such as campaign financing superiority, greater name recognition, and established campaign infrastructure.
Step-by-step explanation:
In most congressional elections, challengers lose against the incumbents. This trend is a result of the incumbency advantage, which includes factors such as campaign financing, name recognition, existing campaign organizations, and the incumbents' ability to connect with voters through mechanisms like franking privileges. For example, in 2020, the average Senate incumbent raised a significant amount more in campaign finances than their challengers. Additionally, incumbents often have greater name recognition, resources to manage constituent casework effectively, and an existing war chest for campaigning. These advantages discourage many potential strong contenders from entering races against incumbents, further solidifying the incumbents' likelihood of reelection.