WASHINGTON (REUTERS) - Republican candidate Donald Trump said on Monday he expected widespread voter fraud in the Nov 8 United States presidential election, ramping up his warning of a rigged election without providing any evidence and despite numerous studies that show the electoral system is sound.
Trump has tried to whip up fears of a flawed election as he has fallen back in opinion polls against Democrat Hillary Clinton. He is also strongly denying allegations from multiple women that he has sexually assaulted or otherwise behaved inappropriately with them.
"Of course there is large-scale voter fraud happening on and before election day. Why do Republican leaders deny what is going on? So naive!" Trump said on Twitter on Monday.
Trump, a New York businessman making his first run for public office, has worried a number of Republicans over his allegations of election fraud. Some of them have urged him publicly to show proof or drop the assertions. Early voting and voting by mail have begun in many states.
While Trump's vice presidential running mate, Mike Pence, and his campaign manager, Kellyanne Conway, have tried to reshape the candidate's comments as being aimed at an unfair news media, Trump's own words have targeted the legitimacy of the election system.
Even after Pence said in a televised interview on Sunday that Trump would accept the results of next month's election, Trump tweeted that the "election is absolutely being rigged by the dishonest and distorted media pushing Crooked Hillary - but also at many polling places - SAD."
Trump has tried to portray Clinton, a former US senator and secretary of state, as a corrupt lifelong politician who is vested in preserving the status quo.
His campaign pounced on the release on Monday of FBI documents that cited an FBI official as saying a senior State Department official sought to pressure the bureau in 2015 to drop its insistence that an email from Clinton's private server contained classified information. Clinton's decision to use a private server while secretary of state from 2009-13 has drawn criticism that she was careless with national security.
The country's top elected Republican, House of Representatives Speaker Paul Ryan, has tried to counter Trump's message about election fraud. Spokeswoman AshLee Strong said on Monday that Ryan "is fully confident the states will carry out this election with integrity."
Ryan last week distanced himself from Trump, saying he was going to focus his election campaign efforts on trying to preserve the Republican majorities in Congress.
In the traditionally closely fought state of Ohio, the top elections official, a Republican, said concerns about widespread voter fraud were simply not justified. "I can reassure Donald Trump: I am in charge of elections in Ohio and they're not going to be rigged, I'll make sure of that," Ohio Secretary of State Jon Husted told CNN.
Numerous studies have shown that voter fraud in US elections is very rare, according to the Brennan Center for Justice at New York University School of Law. In a report titled The Truth About Voter Fraud, the centre cited voter fraud incident rates between 0.00004 per cent and 0.0009 per cent.
An August study by The Washington Post found 31 credible cases of impersonation fraud out of more than 1 billion votes cast in elections from 2000 to 2014. Arizona State University studies in 2012 and 2016 found similarly low rates.
"Despite this overwhelming evidence, claims that voter fraud is rampant consistently garner media attention, because perceived threats to electoral integrity - even those with no basis in fact - frighten voters by striking at the core of our democracy," Brennan Center counsel Jennifer Clark wrote in a blog last month.
Clinton campaign manager Robby Mook told reporters that Trump's assault on the voting system was an act of desperation. "He knows he's losing and is trying to blame that on the system. This is what losers do," Mook told reporters. "It's not true. The system is not rigged."
The RealClearPolitics average of national opinion polls put Clinton currently leading Trump by 5.5 percentage points, at 47.7 per cent support to his 42.5 per cent.
Trump's campaign has been struggling with sexual misconduct allegations from several women since a 2005 videotape emerged on Oct 7 showing him boasting about groping and making other unwanted sexual advances on women. "Can't believe these totally phony stories, 100% made up by women (many already proven false) and pushed big time by press, have impact!" Trump said in another Twitter post on Monday.
Trump has repeatedly denied the allegations but has not provided any proof they are false.
On Sunday night, Trump blamed "animals representing Hillary Clinton" and Democrats in North Carolina for an overnight attack on a local Republican Party headquarters in Hillsborough.
Local, state and federal investigators were sifting through evidence on Monday, trying to narrow the time frame of the incident and looking for clues about who was behind the attack.