In United States politics, a ranking member is the second-most senior member of a congressional or state legislative committee from the majority party.
Another usage refers to the most senior member of a congressional or state legislative committee from the minority party. This second usage, often used by the media, should properly be referred to as the ranking minority member. On many committees the ranking minority member, along with the chairman, serve as ex officio members of all of the committee's subcommittees.
When party control of a legislative chamber changes, a committee's ranking minority member is likely, though not assured, to become the next chairman of the committee, and vice versa.
Congressional usage
Four Senate committees refer to the ranking minority member as Vice Chairman. The following committees follow the Chairman/Vice Chairman structure for the majority and minority parties.
Other Senate committees refer to the ranking minority members as Ranking Member.
The House of Representatives does not use the term vice chairman for the ranking minority member, though some committees do have a vice chairman position, usually assigned to a senior member of the majority party other than the chairman. House committees that follow this structure are:
Joint Committees of the House and Senate operate in much the same way, with a chairman and vice chairman from the majority party, alternating between a member of the House and a member of the Senate, and often two ranking members from both bodies.