Donald Trump. REUTERS/Jonathan Ernst As Election Day nears and Donald Trump continues to trail Hillary Clinton in the polls, he began Monday morning by promoting the idea that the election is "rigged" and that there is "large-scale voter fraud" happening.

Trump tweeted: "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!"

He wrote in a subsequent tweet: "We have all got to come together and win this election. We can't have four more years of Obama (or worse!)."

Recent studies have yielded few instances of modern voter fraud in the US. A 2014 investigation by Loyola Law School professor Justin Levitt found just 31 cases of voter impersonation in US elections from 2000 to 2014.

But Trump's concerns about election fraud seem to be resonating with voters who support him.

A Politico/Morning Consult poll released Monday found that 48% of Trump supporters said they were "not too" or "not at all" confident that votes would be accurately counted on Election Day, and 81% of Trump supporters said they believe the election could be "stolen" from Trump as a result of voter fraud.

Trump has been slipping in the polls ever since a tape leaked that showed him boasting about groping women and kissing them without their consent. In the Politico/Morning Consult poll, Clinton expanded her lead to 6 points in a four-way race.

Since the tape came out, several women have come forward and leveled various accusations of sexual misconduct against Trump.