Which factor generally favors non-incumbent challengers in Congressional elections over incumbent candidates?

sway among discontent voters

Explanation:

Non-incumbent challengers refers to the candidates that are not currently holding the position and aiming for the next term.

One of the most effective method that non-incumbent tend to use to take the position is by highlighting the failures that is caused by current position holder. Creating public awareness about such failures will create discontent among the voters toward the current holder and make them become more likely to choose for non-incumbent with the hope to change the situation.