"He would plead with Americans to recognize that the caustic, destructive language emanating from our current president is sullying the dream that America once was," Patti Davis wrote.
She said Reagan would have been concerned in particular with Trump's freewheeling rhetoric on foreign policy, his constant attacks on the media and his hardline approach to immigration.
Davis also said her father would have taken issue with Congress for not reining in Trump's presidency.
"He would be appalled and heartbroken at a Congress that refuses to stand up to a President who not only seems ignorant of the Constitution but who also attempts at every turn to dismantle and mock our system of checks and balances," she wrote.
For his part, Trump has pointed to Reagan on several occasions, invoking the former Republican president's statements on Twitter for years and more recently comparing questions over his own mental stability to those Reagan faced.