Historically, congressional leaders in the US have an extremely high reelection rate due to a very high incumbent advantage. Reelection rates for congressional leaders tend to fall within a range of 85-95%.
According to the Congressional Research Service, "The average length of service for Representatives at the beginning of the 112th Congress was 9.8 years (4.9 terms); for Senators, 11.4 years (1.9 terms)." (http://tinyurl.com/a2nhb6e)
While some argue that they would be less effective legislators if their terms were limited, it is this lack of term limits that allows them to become relatively uncontested even as they behave as hyperpartisans, neglecting their constituencies and favoring agendas pushed by powerful corporate lobbies.
Congressional term limits means better representation