The original succession act designated the Senate president pro tempore as the first in line to succeed the president should he and the vice president die unexpectedly while in office. If he for some reason could not take over the duties, the speaker of the house was placed next in the line of succession. In 1886, during Grover Cleveland’s administration, Congress removed both the Senate president and the speaker of the house from the line of succession.
From that time until 1947, two cabinet officials, (their order in line depended on the order in which the agencies were created) became the next in line to succeed a president should the vice president also become incapacitated or die. The decision was controversial. Many members of Congress felt that those in a position to succeed the president should be elected officials and not, as cabinet members were, political appointees, thereby giving both Republican and Democratic parties a chance at controlling the White House.
In 1945, then-Vice President Truman assumed the presidency after Franklin Roosevelt died of a stroke during his fourth term. As president, Truman advanced the view that the speaker of the house, as an elected official, should be next in line to be president after the vice president. On July 18, 1947, he signed an act that resurrected the original 1792 law, but placed the speaker ahead of the Senate president pro tempore in the hierarchy. Truman’s critics at the time claimed that the president did so because he had a close friendship with then-Speaker Sam Rayburn, and a less congenial relationship with Kenneth McKellar, the president pro tempore.
Fortunately for the country, there has never been an instance in which the presidency has had to pass to anyone other than the vice president.