TORONTO -- When outgoing U.S. President Donald Trump tweeted earlier this month that he will not be attending president-elect Joe Biden's inauguration on Jan. 20, he joined a small but infamous group of other presidents who skipped the ceremony in the past.

There are some who think that Trump's decision may be for the best.

"If he had announced soon after the election that he had lost and had decided to go to the inauguration, that's sort of the traditional way of doing it. And I think it would have been seen in a very, very positive light," said Kevin McMahon, a political science professor at Trinity College in Hartford, Conn., in a telephone interview with Thursday.

McMahon said the fact that Trump chose not adhere to tradition "will send a different message and [be seen] differently historically," but that ultimately, his decision not to go is "probably in the best interests of this transition from one administration to the other,” McMahon said. 

While the tradition for the outgoing president to welcome the incumbent to the White House and then ride together to the U.S. Capitol building has been ongoing for decades, Trump is not the first president to not attend the ceremony.

Three other sitting presidents have not attended their successors’ inauguration, and two others, Martin Van Buren and Woodrow Wilson, “were inside the U.S. Capitol signing last-minute legislation but did not attend the public ceremony outside,” according to the White House history website, which is run by the White House Historical Association.  

Here are the presidents who skipped out on inauguration day, for various reasons:

Richard Nixon

The only president to resign from office, Richard Nixon skipped out on the 1974 ceremonies, leaving the White House before then-Vice President Gerald Ford was sworn in.

“Ford is his vice president. He actually chooses Ford. Right? So I don't think there's any expectation that he be there given that he resigned from office,” McMahon said.

“I think the idea there was that he was leaving the office and this was a way for Ford to move on, to be his own person.”

“While the sitting president was not there, this occasion was considered a presidential succession and not a traditional inauguration,” the White House history website said of the Nixon-Ford transition.

Andrew Johnson

Andrew Johnson, who retains the dubious honour of being the first American president ever impeached, stayed at the White House to sign legislation during the 1869 inauguration of Gen. Ulysses S. Grant.

McMahon says that’s not surprising given that Johnson was seen as “illegitimate.”

“Some part of this [his absence] deals with being considered a less legitimate president because he became president after Lincoln's assassination,” McMahon explained.

“Vice presidents who took over the office, particularly in the 19th century, were viewed as less legitimate because they did not win the office. In Andrew Johnson's case, Lincoln was a Republican, Johnson was a Democrat, and he was chosen as a way to unify the country. And quickly into his presidency there was a hostility between him and the Republicans in the Congress.”

McMahon said that Johnson was only one vote short of being removed after being impeached, and “it’s not surprising” that he would not attend the inauguration, “given how he was treated by Republicans while president.”

John Quincy Adams

Son of former president John Adams, John Quincy Adams – who won his election in 1824 by a one-vote electoral college margin over Andrew Jackson - refused to attend his eventual successor Jackson’s inauguration in 1829.

McMahon says that Quincy Adams’ rise to power was “almost a fluke” with the one-vote margin, and that he “lost the popular vote by a massive amount.”

“Jackson was the defeated candidate and then comes back and wins….and there’s not a lot of support for John Quincy Adams,” McMahon said, adding that all those factors together could have influenced his decision not to attend the inauguration – but that there is no official reason recorded for his absence.

“Like his father, John Adams, President John Quincy Adams did not attend the inauguration of his successor. President-elect Andrew Jackson arrived in Washington on February 11, 1829. He did not call on President Adams, nor did Adams invite Jackson to the White House. Later that month, President Adams moved to a mansion on Meridian Hill in Washington, D.C., and officially departed the White House on the evening of March 3, the day before the inauguration of President Jackson,” the White House history website explains.

John Adams

The only Federalist president ever elected, and the first U.S. president to inhabit the White House, John Adams refused to attend his successor Thomas Jefferson’s inauguration in 1801.

“President John Adams did not attend Thomas Jefferson’s inauguration. He departed from the White House at 4 a.m. the morning of his successor’s inauguration. While Adams never recorded why he left, he may have wanted to avoid provoking violence between Federalists and Democratic-Republicans, as this was the first time the presidency was transferred to an opposing party. He was also never formally invited by Jefferson and perhaps didn’t want to impose,” the White House history website says.

McMahon says the answer also may be as simple as Adams was “the first president to lose an election” – and therefore the tradition of attending his successor’s inauguration wasn’t quite established yet.