Las Vegas - Donald Trump refused on Wednesday to say that he would respect an eventual Hillary Clinton victory in the US presidential race, threatening at his final debate with the Democrat to keep the country "in suspense".Trump - perhaps the most controversial presidential candidate in half a century - came into the third televised debate of the 2016 campaign in Las Vegas looking to right his campaign with just 20 days to go before Election Day.Dogged by allegations of sexual misconduct, trailing in the national polls, and losing ground in key swing states, the 70-year-old Republican real estate mogul was looking to capitalise on his last major chance to woo undecided voters.In an extraordinary exchange, a combative Trump doubled down on his claims that Clinton's campaign team and the media were attempting to rig the vote."The media is so dishonest and so corrupt and the pile-on is so amazing," Trump said, referring in part to widespread press reports citing women accusing him of sexual assault, which he also said were drummed up by Team Clinton.'Fake' votersHe went on to allege that "millions" of fake voters had been registered and that the 68-year-old Clinton should not even have been allowed to run because she mishandled classified State Department e-mails.Clinton declared herself "appalled" by what she said was an attack on 240 years of US democracy and, quoting her onetime rival Bernie Sanders, called Trump the "most dangerous person to run for president in the modern history of America".Asked by moderator Chris Wallace of Fox News whether despite his doubts he would commit to recognising the result of the November 8 vote no matter what, Trump said: "I'll tell you at the time.""I'll keep you in suspense, OK?" Trump, who once hosted the reality television show The Apprentice, said to gasps from the audience.The unprecedented assault on the conventions of the process was only one of a series of ferocious clashes, as two stony-faced candidates faced off from behind podiums with little stagecraft on everything from immigration to Syria.At one point, Trump broke into one of Clinton's responses to call her "such a nasty woman". The candidates took and left the stage without shaking hands.Ripped from womb The Democratic former secretary of state scored an early hit against the Republican property mogul, alleging that Russian President Vladimir Putin was backing his run for office.Clinton cited reports from US intelligence agencies that Russian cyber attacks had targeted her party and campaign and demanded that Trump condemn the interference."They have hacked American websites, American accounts of private people, of institutions," she declared. "Then they have given that information to WikiLeaks for the purpose of putting it on the internet."The Manhattan billionaire dismissed the intelligence reports, declaring: "Our country has no idea."Trump argued that he might negotiate better relations with Moscow than Clinton would, declaring: "Putin, from everything I see, has no respect for this person."Clinton's response was sharp: "Well, that's because he would rather have a puppet as president of the United States."Trump blustered back: "No puppet. You're the puppet."In what has been a toxic campaign, the two White House hopefuls got off to a subdued but oddly substantive start to the debate, compared to previous brawls.They were asked about their vision for the Supreme Court, prompting Clinton to argue the election was about "what kind of country are we going to be". She insisted gay rights and women's rights must not be rolled back. Trump echoed conservatives who believe "the Supreme Court is what it's all about", vowing to appoint anti-abortion justices who would also protect gun rights."If you go with what Hillary is saying, you can take the baby and rip the baby out of the womb of the mother just prior to the birth of the baby," he said."Using that kind of scare rhetoric is just terribly unfortunate," Clinton responded. 'New Brexit' Pundits have declared the presidential race all but over after the provocative billionaire attacked leaders of his own party and obliterated the normal rules of political decorum. In response to Trump's attacks on the legitimacy of the vote, President Barack Obama has implored him to "stop whining" and Senator Elizabeth Warren told him to "put on your big boy pants" The White House is increasingly concerned that Trump and his most passionate supporters will not recognise the election's outcome, plunging the country into a political crisis, and his debate response on Wednesday did nothing to dispel that fear.Trump predicts an electoral surprise, or "new Brexit", when Americans vote next month.But it remains an open question whether any of these stunts will have a positive impact with voters.Clinton leads by more than six points in an average of national polls compiled by RealClearPolitics.Women especially have thrown their support to the former secretary of state, senator and first lady, who is poised to become the first female president in American history.A Quinnipiac University poll showed she is winning with female voters by 52% to Trump's 37%.