‘Should” as in “deserves to”? Or “should” as in “has the chance to”? Semantics aside, none of this year’s best picture nominees have had such a fall from grace as Green Book, which – after its debut at the Toronto film festival – looked to have all the attributes of a solid-gold awards-season success. With a top-notch cast, empathetic film-making and a hugs-all-round message that everyone could get behind, it looked like one of those gets-you-by-the-throat liberal juggernauts, this year’s Hidden Figures maybe, or Spotlight.

But then, like a wiseguy fitted with a concrete overcoat, Green Book’s chances sank like a stone. You can’t pretend to be authoring a plea for social tolerance if you are enthusiastically backing one of Donald Trump’s nasty racist lies; nor can you claim to be much of a liberal if your idea of a laugh is frat-boy harassment. Worse, if the family of the man you are using to validate your credentials say your story is basically not true, you are in trouble. Though not necessarily fatally so: plenty of good films have iffy people around their edges.

What I suspect has hurt Green Book more – especially with the younger, savvier Oscar-voting demographic – are all the complaints about white-saviour tropes. And for good reason. Although the film tries to suggest there’s a mutual back-and-forth – Doc Shirley helps Tony Lip class up his life, just as Lip helps Doc get in touch with his earthier side – the fact that the Italian American hoodlum type, Vallelonga, is the lead (no surprise since his son Nick is one of the film’s writers and producers) means it’s his perspective that dominates, his character progression that ballasts the film. Doc writes Tony’s love letters, teaches him to appreciate great music and impresses with his dedication to standing up for himself. But it’s Tony who gets the real glory by seeing off aggressive good old boys in a bar, turning Doc on to Little Richard, Chubby Checker and Aretha Franklin, and in a somewhat skincrawling climax, acting like he’s “allowed” Doc to impress the patrons of a black music joint with a piano freakout.

Keep things afloat … Green Book. Photograph: Dreamworks

So is Green Book that bad? Does it have any redeeming features? Well, the basic skill that went into its making is unarguably impressive. As our critic Peter Bradshaw pointed out, Viggo Mortensen and Mahershala Ali are both very good, keeping the whole thing afloat. Peter Farrelly, if we ignore the harassment issues, knows what he’s doing, picking great line readings and barely putting a foot wrong with an elegant mise en scène. Although the script’s shortcomings have been well-discussed, there’s interesting material on the mafioso lifestyle, and how getting involved in it is a choice. (If you think of Green Book as a sort of low-intensity Sopranos-esque gangster pic, where the mafioso learns life lessons, it starts to seem a little less disreputable.) And while Tony Lip’s “I’m blacker than you” line is idiotic, Green Book highlights an interesting disjunction between the deep-south hillbilly culture and the New York Italian Americans: whiteness is not necessarily a homogenous cultural position, a subtle and challenging point in the era of identity politics.

Green Book has been holed below the waterline, and taking on water fast. But that doesn’t mean it can’t make the harbour.