Former President Barack Obama reportedly revealed to supporters this week whats keeping him awake at night.

Obama, during a virtual fundraiser for presumptive Democratic nominee Joe Biden on Tuesday, said he feared the prospect of President Donald Trump questioning the legitimacy of the 2020 election, The New York Times reported on Thursday.

In the online event with actor George Clooney, Obama also reportedly expressed grave concern about Republican voter suppression efforts.

In public, Obamas criticism of his successor has mostly been muted, and he rarely mentions Trump by name. In private fundraising appearances, however, Obama has explicitly called out Trump multiple times, according to the Times.