Donald Trump warned of ‘bedlam” if election results were delayed inordinately while his Democratic challenger for the White House Joe Biden, and his former boss Barack Obama, attacked and mocked the US president in their first joint campaign appearances.

“November 3rd is going to come and go, and we’re not going to know. And you’re going to have bedlam in our country,” Trump said at one of four rallies he addressed in Pennsylvania, referencing a Supreme Court decision allowing Pennsylvania and North Carolina to count mail-in ballots received even after the close of polling on November 3. “You’re going to have this period of nine days, seven days.”

Trump went on to suggest “bad things” could happen, echoing unfounded fears he has raised before of election fraud. He has notably been unwilling to commit himself to a peaceful transfer of power if he loses, citing his doubts about mail-in voting which is being used widely because of Covid-19.

There are concerns Trump could refuse to accept the election outcome if he loses and may not leave office.

Some of his supporters are actually prepared to help him if he did indeed refuse to go. Ryan Slingerlane, a New Yorker who drove four hours to attend his first Trump rally, said in Reading, Pennsylvania, that although he did not foresee the president losing, “if he does, and he doesn’t want to go, I will have his back a 1,000%, a 100,000% and … there is nothing I wouldn’t do if he decided to stay in office”.

There are fears of unrest, including violence in the days after polling. Shops and business establishments have been boarding up in Washington DC and some other cities with memories still fresh of large-scale looting and vandalism during the initial days of recent anti-racism protests. Retail giant Walmart has already removed guns and ammunitions from its shelves in some areas.

Biden and Obama, however, focused on the race in hand at the rallies in Michigan, a battleground state, and their key argument for voting Trump out of office: his handling of the Covid-19 epidemic, which has killed more than 230,000 Americans and infected 9 million and is now ripping through the country again.

Biden slammed the president, saying once again he had “waved the white flag of surrender to the virus”, which he won’t do if elected. “One Day One of my presidency, we will put into action the plan I have been talking about for months: Masking. Social distancing. Testing. Tracing,” he said.

Obama also attacked Trump for this handling of the pandemic, but without pulling his punches. He spoke of the president’s “obsession” with crowds and accused him of holding rallies that, new research shows, have left a trail of Covid-19 infections.

“Does he have nothing better to worry about? Did no one come to his birthday party when he was a kid? What’s with the crowd size?” Obama said.

Both presidential candidates will be in other background states with their surrogates on Sunday and Monday, wrapping up their closing arguments for the close of polling on November 3.

Record turnout is expected this cycle, with more 91 million Americans having voted already, which is two-thirds the total votes cast in 2016. Early voting is more popular among Democrats and the current turnout is expected to help them, but the Trump campaign hopes to make up with a big turnout on Election Day.

Daniele Delehanty, a retired flight attendant, will be one of them. “It seems right to vote on Election Day,” she said at Trump’s rally in Reading, when asked why she did not vote early.