Clooney expressed reservations about the campaign at least once that year, even as he used his star power to raise millions of dollars for Clinton.
Yes, he told NBC News in April: $353,000 a head for dinner with Clooney and Clinton at the actor's Los Angeles home was "an obscene amount of money."
But, Clooney added, quite a lot of that obscene amount would go not to Clinton, but to down-ticket Democrats who would help her govern.
"The Clinton campaign has not been very good at explaining ... this," he noted as an aside.
Still, as Clinton and Trump each moved toward securing their parties' nominations, Clooney's confidence rose.
"There's not going to be a President Donald Trump," he said at the Cannes Film Festival in May 2016. "That's not going to happen."
And then a few months later - well, we know what happened.
While Clinton resorted to the yogic method of alternate nostril breathing to cope with the shock of her loss, Clooney made abrupt edits to his upcoming satire, "Suburbicon" - to match the mood of a "darker and angrier" country, he later explained.
In the year since election night, Clinton wrote a book about her loss, called "What Happened." And she blamed herself, yes, but also Sanders, and the media, and an FBI director who renewed public interest in an investigation into Clinton's email server at a crucial point in the campaign.
And whom did Clooney blame? He hasn't said that much, but he gave an interview to the Daily Beast this week. It was mostly about his movie, but somehow his fundraising and endorsements for a failed presidential candidate came up: "Do you feel like history will look kindly on Hillary Clinton?"
And just as he'd done in his letter backing the candidate, more than a year ago, Clooney expressed his disappointment briefly and bluntly.
"She was more qualified than even her husband was when he was elected president," he said. "But she's not as good at communicating things. That's simply true. When she got up and gave a speech, it didn't soar."
Clooney called Clinton "the right person to side with." But he admitted: "It was frustrating because I never saw her elevate her game. I never saw it. And I had a lot of liberal friends who were like, 'She's not good at this.' And I see that, and I understand it."
The past year seems to have changed Clooney, who was once so certain that Trump's fearsome rhetoric would never best Clinton's merits - even if her speeches were middling.
"I think that she wasn't particularly good at articulating the things that she wanted to do," Clooney told the Beast. "And unfortunately we live at a time right now where articulating what you want to do is more potent in the electorate than the other way around."
He added this thought:
"Don't you think the next Democrat who runs should just run with a blue hat that says, 'Make America Great Again?' "