Joss Whedon pulled out all the stops to get out the vote for Democratic presidential candidate Hillary Clinton ahead of Election Day, but to no avail — and now the writer-director says Republican President-elect Donald Trump “cannot” be allowed to serve even his first term in office.

“This is simple,” the 52-year-old Avengers director wrote on Twitter Monday. “Trump cannot CANNOT be a allowed a term in office. It’s not about 2018. It’s about RIGHT NOW.”

This is simple: Trump cannot CANNOT be allowed a term in office. It's not about 2018. It's about RIGHT NOW — Joss Whedon (@joss) November 14, 2016

Whedon — who only recently returned to Twitter after having deleted his account last year following feminist backlash against his Avengers sequel — has spent the days since the election challenging Trump on social media.

“Letting [T]rump take office means burying democracy. Letting him take it without the popular vote means burying it alive,” the director wrote on Sunday.

“Is this all worse for the young ppl who are stunned or for those of us who’ve watched it since Reagan like a slow motion car crash?” he wrote in an earlier post.

RULE: we need to establish a clear chain of command from trump's cabinet down to the republican house by human centipedeing all of them — Joss Whedon (@joss) November 12, 2016

Trump's enemies list is the school musical all over again – my stomach is in knots cuz when they post it i just KNOW i won't see my name — Joss Whedon (@joss) November 12, 2016

WE HAD THE TIME MACHINE AND WE STILL DIDN'T STOP HITLER — Joss Whedon (@joss) November 11, 2016

Whedon has also called on Clinton supporters to “keep protesting.” In the days since Trump’s election victory, demonstrators have taken to the streets in New York City, Portland, Los Angeles, San Francisco, Boston and Washington D.C., among other cities, to protest the results.

Voter suppression

Russian hacking

FBI collusion

He has the office

BUT HE IS NOT WELCOME HERE

Keep investigating

Keep protesting#NEVERtrump — Joss Whedon (@joss) November 11, 2016

It is not clear what Whedon (or anyone else) could do to prevent Trump from serving his first term in office, though some have attempted to do just that; since election night, more than four million people, including some celebrities, have signed a petition calling on electors in the Electoral College to disregard the will of their states’ voters and instead make Clinton president.

The Electoral College will officially cast their votes on December 19.

Whedon, who restored his Twitter account in September, was a high-profile celebrity supporter of Clinton.

In September, the director pulled together dozens of celebrities — including Avengers cast members Robert Downey Jr., Scarlett Johansson, Mark Ruffalo and Don Cheadle — for a voter registration PSA aimed at encouraging younger voters and millennials to turn out for Clinton.

The PSA, which was viewed nearly eight million times before Election Day, was the first video released by Whedon’s Save the Day PAC, which he had launched ahead of the election. In an interview with Buzzfeed that month, Whedon said the video was part of his effort to stop Trump, whom he called “orange Muppet Hitler,” from reaching the White House.

However, in response, advertising company Brabender Cox released a send-up of Whedon’s PSA that featured ordinary, non-famous Americans thanking celebrities for reminding them the date of Election Day and of the stakes involved in the decision. The video mocking the celebrities also subsequently went viral.

Follow Daniel Nussbaum on Twitter: @dznussbaum