Barbra Streisand -- a prominent Democrat -- went after the moderators for letting Donald Trump change the subject whenever he wanted in her view ... calling the proceedings unfair.

Meanwhile, fellow Dem John Cusack pointed to the Donald's newly found convict status ... and blamed CNN that "abdicated every definitional responsibility."

Bette Midler, Jesse Williams, Mark Hamill and 'Star Trek' actress Jeri Ryan also took shots at the former prez and the moderators ... though they weren't exactly singing Biden's praises.

Don't think DT didn't have any H'wood stars in his corner though ... 'cause the former president's performance got its laurels from popular Tinseltown Republicans.

Roseanne Barr -- always outspoken and quick to joke about liberals -- didn't crack any jokes Thursday ... saying, "I take no happiness in this debate. Biden is clearly not here. This is sad."

Meanwhile, Caitlyn Jenner took a harsher stance toward JB ... pointing to his "major mental decline" -- and calling him a complete failure. Comedian Jamie Kennedy cracked a joke about Joe's mental acuity, adding the Prez couldn't even sign a person up for Netflix let alone run a country.

In case you missed it ... Biden's performance at the debate was widely panned ... he struggled to answer questions in a barely audible, hoarse voice -- and at one point he completely lost his train of thought.

Flash CNN polling says Trump had the better performance, with 67% saying he won the bout with Biden.

About 4 months until the election ... anyone getting nervous yet???