Former President Barack Obama posted a video on National Voter Registration Day on September 22 and called on his followers to vote for Democratic candidate Joe Biden to ensure that "our democracy will last forever".
In a video posted on Twitter, Trump argued that the risks in November were "greater than Joe or the person he is replacing."
"What is at stake is whether our democracy will last a long time," The Hill quoted Trump as saying in the video. " And those in power hope you are at home."
The comments echoed Trump's comments in an online message at the Democratic National Convention last month as he viewed his successor as a threat to democracy and the rule of law.
"For nearly four years, he has shown no interest in work; no interest in finding common ground; no interest in using his power to help anyone other than himself and his friends; no interest in considering the president's job as anything other than a reality show that he can use to attract the attention he longs for," Trump said in his speech at the congress.
National Voter Registration Day, held on September 22, is a nonpartisan campaign for voters to register to vote in US presidential elections, and has been held since 2012. Nearly 3 million Americans have registered to vote as part of the event since it began, according to the campaign's website.