With senior members engaged in difficult re-election efforts, the Congressional Black Caucus is facing an existential threat to its clout. The tough races come as the caucus also faces new challenges to its identity, including how to assimilate black Republicans and whether - and how - to criticize President Barack Obama, the first African-American to hold the office.

At the heart of the CBC's challenges are two high-profile Democratic Members, Reps. John Conyers (Mich.) and Charlie Rangel (N.Y.), who are in unusually stiff primary races. The pair, the second and third most senior House Members, have served a combined 88 years in Congress. 

Detroit-area Democrats say Conyers could face one of the toughest re-election matches of his career. Several Democrats will challenge him in the Aug. 7 primary, including state Sens. Glenn Anderson and Bert Johnson. When local Republicans redrew the Congressional map last year, they dismantled the two Detroit-based House seats represented by Conyers and freshman Rep. Hansen Clarke (D), another CBC member. As a result, Conyers will seek re-election in mostly new turf.