The 25th Amendment, ratified in 1967, is one of the most important amendments to the Constitution. It establishes the procedures for presidential succession and fills a critical gap that was left open by the Founding Fathers.

The amendment was prompted by the assassination of President John F. Kennedy in 1963. Vice President Lyndon Johnson became president, but there was no clear line of succession if something happened to him. The amendment addresses this by stating that the vice president would become president if the president died, resigned or was removed from office.

The 25th Amendment also allows for the appointment of a new vice president if the office becomes vacant. This was necessary because there had been several instances in which the vice president had died or resigned.

Since ratification, the 25th Amendment has been used several times. In 1974, Vice President Gerald Ford became president when Nixon resigned in the wake of the Watergate scandal. In 1981, Vice President George H.W. Bush became president (temporarily) when Ronald Reagan was shot by a would-be assassin.

The amendment has also been invoked when a president is incapacitated. In 1985, Reagan underwent surgery and was temporarily unable to perform his duties. Vice President Bush became acting president during that time. The 25th Amendment is an important part of our Constitution that ensures the continuity of our government in the event of a presidential vacancy.

Something interesting is happening in President Biden’s tenure. The same Joe Biden — no more or less capable, as CNN points out — looks different:

“But suddenly, images of Biden as a feeble septuagenarian atop a mismanaged White House have given way to those of an experienced leader, smiling behind aviator sunglasses, whose battle-tested team has delivered on a range of national priorities. A winning streak does that for you.”

The thing with any winning streak is that it eventually ends. While public perceptions and approval ratings of any president can ride one or more nice waves during their four or eight years in office, eventually the waves dissipate and voters see the president in a new light … one that might still shine the light on some key wins but also the reality of the cyclical tough times that every president and every administration deals with.

The reality remains that the median age of a U.S. president at his inauguration is 55. Biden became the oldest president at his inauguration at 78 years and 61 days. Biden was, in fact, older at inauguration day than the previous oldest president, Reagan, was when he left office: 77 years and 349 days.

Suppose we reach the point during Biden’s administration when people are again focusing on perceptions of him as older, weaker and frail, there is no doubt that some will again raise the specter of the constitutional amendment that addresses replacing a president when she or he is unable to serve. Yet there are important reasons the 25th Amendment is used so infrequently.

First, the amendment is designed to address situations in which the president is unable to perform his or her duties, and most presidents can fulfill their duties without issue. Public perception is one thing; the actual inability to perform the job daily is entirely another.

Second, the amendment requires the support of the vice president and a majority of the Cabinet, which can be difficult to obtain. Finally, invoking the amendment can be seen as an admission of failure, which presidents are often reluctant to do.

History has taught us what a serious thing it is to invoke the 25th Amendment. Doing so not only sends a signal to Americans about the health of their president, it sends a message to the world that this is a moment in which the American government may be vulnerable, and this is something no one in Congress should want to do.