In the annals of 20th century American history, the name of Dwight David Eisenhower will go down in many ways, for many things, but one goes largely overlooked:  unlike his predecessors, not only did "Ike" want to address the matter of presidential succession, but he had a plan in place to do so.

Early in his administration and under the guidance of Attorney General Herbert Brownell, Eisenhower and Vice President Richard Nixon reached a private agreement which consisted of four short paragraphs:

"The President and Vice President have agreed that the following procedures are in accord with the purposes and provisions of Article II, Section 1 of the Constitution, dealing with Presidential inability.  They believe that these procedures, which are intended to apply to themselves only are in no sense outside or contrary to the Constitution but are consistent with its present provisions and implement its clear intent.

(1)  In the event of inability the President would - if possible - so inform the Vice President, and the Vice President would serve as Acting President, exercising the powers and duties of the office until the inability had ended.

(2)  In the event of an inability which would prevent the President from so communicating with the Vice President, the Vice President, after such consultation as seems to him appropriate under the circumstances, would decide upon the devolution of the powers and duties of the Office and would serve as Acting President until the inability had ended.

(3)  The President, in either event, would determine when the inability had ended at that time would resume the full exercise of the powers and duties of the Office."

This agreement ultimately would lay the groundwork for Sections 3 and 4 of the 25th Amendment, and would be put to the test on three different occasions during Eisenhower's two terms in office.  On September 23, 1955, Eisenhower suffered a heart attack while on vacation which, while not considered severe by today's standards, was still cause for serious concern.

First reported as a "digestive upset," Vice President Nixon was stunned when he received a telephone call from White House Press Secretary James Hagerty with more serious news.  Eisenhower was hospitalized, but thanks to their agreement there was an unofficial answer to two of the key questions:  the President would declare himself unable to discharge the powers and duties of the Presidency if he was of sufficient capability to do so; otherwise, the Vice President, after "appropriate consultation," could do so and take the helm.

While the agreement was never formally invoked following Eisenhower's heart attack, or in June 1956 when Eisenhower was hospitalized for a bowel obstruction, or even on November 25, 1957 when the President suffered a mild stroke, in each case Vice President Nixon nonetheless carried out some of Eisenhower's informal (but not ceremonial) Presidential responsibilities.  An identical agreement would be signed between President John Kennedy and Vice President Lyndon Johnson in 1961, and was in place (but unutilized) on November 22, 1963 when Kennedy was assassinated in Dallas, Texas.