What amendment defines the presidential line of succession in the event of the president's death or incapacitation?

The amendment that defines the presidential line of succession in the event of the president's death or incapacitation is the 25th amendment. Ratified in 1967, this amendment explicitly outlines the procedures for presidential succession and addresses issues related to presidential disability.

The 25th amendment includes provisions for the appointment of a new vice president if that position becomes vacant, as well as processes for the president to voluntarily transfer power to the vice president during times of incapacity. This ensures continuity of government and a clear line of authority, which is crucial during emergencies when the presidency is in flux.

Other amendments listed, such as the 22nd amendment, which limits the number of terms a president can serve, and the 23rd amendment, which grants electors to the District of Columbia, do not pertain to succession. Similarly, the 24th amendment addresses voting rights and election practices, making them unrelated to the issue of presidential succession. Therefore, the 25th amendment is the relevant constitutional measure for handling these specific circumstances concerning presidential leadership.