During an interview with Chris Wallace, Trump claimed that Fox News polls showing him losing to Biden were fake, and declined to answer definitively if he would accept the 2020 election results if he lost.

I have to see. Look, you – I have to see. No, I’m not going to just say ‘yes.’

Trump has repeatedly attacked mail-in voting despite the worsening COVID-19 pandemic, though he used mail-in voting himself. In the lead up to the 2016 campaign, Trump similarly declined to say whether he would accept the election results. Even though he ultimately won, he blamed the loss of the popular vote on mass voter fraud.

During the same interview, Trump bragged about completing a basic cognitive function test.

Business Insider – Trump foreshadows that he could refuse to accept the results of the 2020 election if he loses
Time – ‘I Have to See.’ President Trump Refuses to Say If He Will Accept the 2020 Election Results
Forbes – Pelosi Slams Trump’s Suggestion He Won’t Accept Election Results: ‘He Will Be Leaving’