Biden joins rare group of presidents who choose not to seek re-election

For many voters, this moment in history may feel like a crisis. But America is hardly walking over new ground with a sitting president dropping out of the presidential race.

Not only has it happened before, it's actually happened several times in the not-so-distant past.

With his announcement, Joe Biden joins a rare group of sitting presidents who chose not to seek re-election.

"I shall not seek and I will not accept the nomination of my party for another term as your president," President Lyndon B. Johnson announced 56 years ago, when he told the American people that he would not run for a second term amid the increasingly unpopular war in Vietnam and growing national unrest.

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"Political violence that year, we saw the assassinations of Martin Luther King and Bobby Kennedy. We've seen, of course this year, the assassination attempt on President Trump's slide, we saw divisions and discord and volatility in 1968. We're seeing that again, this year," said ABC News contributor and presidential historian Mark Updegrove.

In 1952, despite leading the country through the end of World War II, Harry Truman also opted not to seek re-election.

Entering the Korean War, among other unpopular decisions, left Truman facing the lowest job approval rating on record at just 22%.

"I have served my country long, and I think efficiently and honestly, I shall not accept a renomination," Truman said. "I do not feel that it is my duty to spend another four years in the White House."

Presidents Teddy Roosevelt and Calvin Coolidge also decided not to run for another term. But Biden's decision stands apart from those of his predecessors -- all of whom served more than four years in office.

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"All of those presidents -- Theodore Roosevelt, Coolidge, Harry Truman, Lyndon Johnson -- all took the presidency upon the death of an incumbent, became president in their own right by getting elected to the office and then declined another term in office. So, this is a little different insofar as Joe Biden, you know, was the candidate in 2020, became president and has opted after one term not to go forward," Updegrove explained.

But now, Democrats are hoping to avoid history repeating, because in the most recent two examples -- when Johnson and Truman (both Democrats) stepped aside, a Republican won the next election: Eisenhower following Truman and Nixon following Johnson.

This will be the first election since 1976 that will not include a Bush, Clinton, or Biden on the ticket.