Washington – Donald Trump has stepped up claims the presidential election will be rigged against him, as polls showed support slipping away from the Republican candidate only three weeks from the vote.The bombastic billionaire fired off a series of erratic Twitter broadsides at his opponent Hillary Clinton and the media over the weekend as tensions mount ahead of the November 8 election."Polls close, but can you believe I lost large numbers of women voters based on made up events THAT NEVER HAPPENED. Media rigging election!" Trump wrote.Some analysts have voiced fears that Trump's repeated claims of fraud could spark violence from his supporters if he loses.After the first election debate, Trump said he would respect the election result. But he backtracked in an interview with the New York Times last month saying, "We're going to see what happens."Trump's running mate Mike Pence however sought to ease tensions, insisting his camp would accept defeat if that's what voters decide.Clinton ahead"We will absolutely accept the results of the election," he told CBS.Pence was asked about a Trump supporter who told a newspaper he planned to go to polling places and make voters "a little bit nervous"."I don't think any American should ever attempt to make any other American nervous in the exercise of their franchise to vote," Pence said.Underscoring how divisive this election campaign has been, a Republican Party office in the southern state of North Carolina was firebombed overnight on Sunday, with the message "Nazi Republicans leave town or else" sprayed on an adjacent building.No one was hurt in the attack, swiftly condemned by Clinton. The attack on the Orange County HQ @NCGOP office is horrific and unacceptable. Very grateful that everyone is safe.— Hillary Clinton (@HillaryClinton) October 16, 2016 "The attack on the Orange County HQ @NCGOP office is horrific and unacceptable," Clinton wrote on Twitter. "Very grateful that everyone is safe."Two polls out on Sunday – taken after a slew of sexual misconduct allegations against Trump that emerged last week – put Clinton ahead.But they did so by vastly different numbers: an ABC News/Washington Post survey had Clinton four points ahead while an NBC News/Wall Street Journal poll put her margin at 11 points.Counting the deadAdding to the polemic over Trump's fraud claims, top adviser Rudy Giuliani told CNN on Sunday – without offering evidence – that Democratic districts are known for counting the votes of dead people.Giuliani claimed that if Republicans "control the inner cities the way Democrats do," then maybe "they'd do as much cheating as Democrats do".Clinton's running mate Tim Kaine, interviewed on ABC, dismissed the claims.Trump is "swinging at every phantom of his own imagination because he knows he's losing," Kaine said.The nation's top elected Republican, House Speaker Paul Ryan, who has declared that he would no longer "defend" the party's nominee, rebuked Trump over his comments questioning the validity of the election process."Our democracy relies on confidence in election results, and the speaker is fully confident the states will carry out this election with integrity," his spokesperson AshLee Strong said in a statement.Final debateThis sparked another Trump outburst at Ryan."The Democrats have a corrupt political machine pushing crooked Hillary Clinton. We have Paul Ryan, always fighting the Republican nominee!" he wrote. Wow, interview released by Wikileakes shows "quid pro quo" in Crooked Hillary e-mail probe.Such a dishonest person - & Paul Ryan does zilch!— Donald J. Trump (@realDonaldTrump) October 16, 2016 As Trump and Clinton prepare for their third and final debate on Wednesday, Clinton is lying low, apparently relying on Trump self-destructing.These are also delicate times for Clinton. As sexual misconduct claims against Trump dominate the campaign, Clinton has appeared reluctant to speak out because she stuck by husband Bill while he was mired in the Monica Lewinsky and other sex scandals when he was president.Nevertheless it is clear that the presidential race is shifting in her favour.The CBS News Battleground Tracker Poll out on Sunday found that, because of a surge in support for Clinton among women, she now leads by six points in a dozen crucial swing states.