Donald Trump has boasted of being an atypical leader but he's now entered a rare club he will definitely not appreciate -- US presidents who have lost reelection.

Since World War II, only two other presidents who sought a second term from voters have failed: Jimmy Carter and George H.W. Bush.

US TV networks called the race on Saturday for Democrat Joe Biden despite the Republican unabashedly seizing on the power of incumbency.

Trump held rallies across the country in front of Air Force One, insisted on putting his name on the 150 million pandemic stimulus checks to Americans and delivered his Republican convention speech at the White House.

His actions sparked accusations Trump violated the Hatch Act, which restricts the use of the federal government for political activity.

"There is a reason why it's unusual for incumbents to be defeated. Incumbents have the ability to use the bully pulpit to their advantage; they can change the storyline," said Matt Dallek, a political historian at George Washington University.

"They have all the trappings of the White House -- executive power, the Oval Office, Air Force One. These are powerful symbols that they have at their disposal."

The White House -- in the words of one of its fictional inhabitants, President Andrew Shepherd in Rob Reiner's "The American President" (1995) -- offers "the single greatest home court advantage in the modern world."

For Trump, the first president never to have previously held elected office or a military leadership position, the White House helped normalize a volatile man better known earlier to Americans as a television celebrity.

However unpresidential in tone his tweets, his every formal event took place behind lecturns bearing the instantly recognizable seal of the US commander in chief.

US presidents enjoy wide leeway on diplomacy and Trump, like his predecessors, eagerly brought foreign leaders before the cameras with him at the White House, including in September when the United Arab Emirates and Bahrain agreed to recognize Israel.

Party unity vital for incumbents

Trump is the first president never to cross 50 percent approval in Gallup polls and was intensely divisive over his nearly four years, with wide opposition to his handling of the pandemic, his abrasive rhetoric and incessant personal scandals.

George H.W. Bush, by contrast, basked in nearly 90 percent approval as he led the first Gulf War in 1991

The difference, Dallek said, is that both Bush and Carter failed to unify their parties.

Carter and George H. W. Bush faced primary challenges from the left and right of their parties respectively that weakened them heading into the general election.

Similarly, Lyndon Johnson -- who technically did not lose reelection but abruptly decided not to seek a second full term in 1968 -- was hit by a revolt on the left over the war in Vietnam.

Gerald Ford, who took over after Richard Nixon's resignation and was never elected nationally on his own, also faced a spirited challenge in 1976 from Ronald Reagan.

Trump, on the other hand, virtually took over the Republican Party, whose 2020 platform said only that it backed his agenda.

"The challengers to Trump really had to go outside the Republican Party," Dallek said.

With Trump's election loss but dominant position in his party, chatter has already begun on whether he would seek an even more unusual feat -- winning a second but non-consecutive term in 2024.

Only one other president in US history has served two terms that were not back-to-back -- Democrat Grover Cleveland, who won his second mandate in 1892, four years after a narrow loss.