Donald Trump's refusal to commit to accepting the outcome of the US presidential election if he loses has been branded plain "dumb" by political observers who warn he has damaged his chances of securing much needed supporters in the campaign's final weeks.
In the final of three televised debates before Americans go to the polls on November 8 the billionaire Republican and his Democrat rival Hilliary Clinton traded blows on issues ranging from the US economy to gun laws, abortion and the civil war in Syria.
But it was Mr Trump's refusal to say that he would accept the result of the election if he is defeated by Mrs Clinton that raised eyebrows around the world.
Dr John Hart, from ANU's School of Politics and International Relations, said it was unlikely Mr Trump would succeed if he tried to challenge the election result in court.
"It was an absolutely dumb move because it put Trump outside the boundaries of what's acceptable in democratic competition in the US," he told AAP on Thursday.
"All the results are certified by Congress. Is he really going to sue Congress?"
Mr Trump has repeatedly complained the election is rigged, alleging the media is conspiring with Mrs Clinton to ruin his campaign.
University of Melbourne associate professor of American politics Dr Timothy Lynch said the presidential race has traditionally culminated in a peaceful transfer of power since 1797 when George Washington stepped down and John Adams took the oath as the second president of the United States.
Mr Trump's promise to "keep you all in suspense" about whether he would continue that tradition smacked of "Apprentice schtick", said Dr Lynch, referring to the billionaire's popular reality TV show.
"The idea how would you hold the greatest democracy to ransom by withholding your approval of the result struck me as absurd," he said.
As they faced off for the final time, Mr Trump again denied claims made by nine women that he groped them without consent, called Mrs Clinton "nasty" and renewed attacks on her use of a private email server while secretary of state.
Mrs Clinton hit back with claims that Mr Trump enjoys belittling women, accused him of being Russian President Vladimir Putin's "puppet" and noted he was hosting the TV show Celebrity Apprentice while she was bringing Osama bin Laden to justice.
Mrs Clinton is likely to maintain the lead over Mr Trump in the opinion polls following the debate, Dr Hart believes.
"What he needed to do was win over some of those wavering people who have come out for Clinton or who have switched from Republican to the Democrats in the past few weeks. But he did nothing to do that," he said.
Dr Lynch said Americans have a choice between an "uninspiring" candidate in Mrs Clinton and an "unfit" one in Mr Trump.
"He didn't do anything to move people who may be wary of him but she has done enough to convince people if they are looking for a saner alternative," he said.
