Former President Jimmy Carter has confirmed that he will attend Donald Trump's inauguration Jan. 20 – the only living former president to do so.

Neither former Presidents George W. Bush nor Bill Clinton have made a final decision as to whether they plan to travel to Washington for the Jan. 20 ceremony.

According to a Politico report , a Bush spokesman said the 43rd president plans to RSVP in the new year, and a source said he is still weighing the decision.

His father, George H.W. Bush, has already sent his regrets, citing his age. The 41st president turned 92 in June.

Neither Bush endorsed Trump in the general election, though former presidents usually lend their support to a potential successor from their own party. But Trump had often been cruel to former Florida Gov. Jeb Bush, one of his opponents in the GOP primary and the son and brother of the ex-presidents.

Meanwhile, Clinton has made public swipes at Trump since election day, when the former reality television star defeated his wife, Hillary Clinton. The bickering is unusual, as former presidents have typically abstained from criticizing their successors.

Sources told Politico that Clinton is considering skipping the swearing-in to avoid an uncomfortable spotlight on his wife, who, as former first lady, would be invited to attend as her husband's guest.

Others say the awkwardness is less important than the symbolic power of a defeated opponent appearing to support the peaceful transfer of power, arguing in favor of both Clintons attending the event.

"It would be especially bad if the Clintons did not attend, because it seems like they do not support the transition of power," one Clinton donor told Politico. "It would be petty, they have to suck it up. She has to go as a former first lady. She will sit prominently."

All four living former presidents – Carter, Clinton and both Bushes – were on hand for President Barack Obama's first inauguration in 2009, although the Bushes did not attend his second ceremony in 2013, citing the elder's health and age.

George W. Bush had the full slate, including Presidents Ronald Reagan and Gerald Ford in 2001, but only Carter, Clinton and his father were in attendance four years later, when Reagan had died and Ford, then 91, was ailing.

Trump has struggled to attract the high-profile guests who usually clamor for tickets to presidential inaugurations and the balls and events that surround the formal swearing-in.

Artists have declined to perform at inaugural weekend events, most recently tenor Andrea Bocelli, who said backlash against reports he was set to perform caused him to reconsider.

The chair of the Presidential Inauguration Committee later said it was Trump who turned down Bocelli's offer, not the other way around.

The Mormon Tabernacle Choir is set to perform, as is Jackie Evancho, the 16-year-old star from reality TV show "America's Got Talent."

Meanwhile, the Radio City Rockettes are also scheduled, apparently over the objections of some of the dancers, many of whom have ties to the Broadway community, which heavily supported Hillary Clinton.

An email sent to the Rockettes by the American Guild of Variety Artists and obtained by Broadway World warned the full-time dancers that a threatened boycott of the inaugural performance was "invalid."

"We have been made aware of what is going on Facebook and other social media, however, this does not change anything unless Radio City has a change of heart. The ranting of the public is just that, ranting. Everyone has a right to an opinion, but this does not change your employment status for those who are full time," the letter read. "If you are not full time, you do not have to sign up to do this work. If you are full time, you are obligated."

Trump lashed out on Twitter Thursday in an apparent response to reports his inauguration was failing to attract performers.