“On the Basis of Sex” faces not just a hard act to follow, but also a hard act to precede.

A decent-ish biopic of Ruth Bader Ginsburg with perhaps the year’s least inviting title, “Basis” likely would fare better if it did not come on the heels of the lively documentary “RBG,” which covered more ground and had the real deal at its center, lifting weights and issuing dissenting opinions. While hitting many of the same highlights, “Basis” generally feels like an imitation. Which it is.

As if things aren’t challenging enough for star Felicity Jones, the movie concludes with a glimpse of the real RBG, ascending the steps of the Supreme Court in the same dress we’ve just seen Jones in and reminding everyone what a singular person Ginsburg is.

“Basis” is best when it sticks to things the documentary couldn’t show because footage doesn’t exist. The home life of Ginsburg and beloved husband Martin (amiable Armie Hammer) is warm and inspirational, emphasizing what a workhorse Ruth was during the years she and Martin were both at Harvard Law School. They had a baby, and Martin was so sick that Ruth had to attend his classes as well as hers, completing the homework for both of them (typewriter buff Tom Hanks is going to love the selection of sleek machines we see Ginsburg perched behind).

Like the documentary, this makes a big deal of the Moritz v. IRS gender discrimination case in which Charles Moritz, the caregiver for his ailing mother, sued to get a tax credit that was being given only to women. It’s the first of the landmark cases tackled by Ginsburg, who was then a teacher, and it comes alive in “Basis,” largely because of former Twin Cities actor Chris Mulkey’s quietly dignified performance as Moritz, who had been told by everybody but Ginsburg that his case was unwinnable.

Brash Ruth and meek Charles couldn’t be less alike, and Mulkey gives the film’s best performance, which may explain why Jones’ scenes with him are her sharpest work.

Elsewhere, Jones is not as successful. Nothing she’s doing suggests the essence of Ginsburg, and Jones doesn’t even attempt the jurist’s distinctive, somewhat nasal Brooklyn drawl, a weird choice because it’s probably one of the most instantly identifiable voices on the planet.

The movie seems to be defensive about that choice, too, because it concludes with an actual Ginsburg voice-over, repeating the oft-quoted line from suffrage leader Sarah Grimké, “I ask no favors for my sex. I surrender not our claim to equality. All I ask of our brethren is that they will take their feet from off our necks.”

I like the film’s insistence that women played an important role in Ginsburg’s life, from the mother who taught her to “question everything” to the daughter who is depicted as being integral to her mom’s involvement in civil rights. Director Mimi Leder makes sure we feel the presence of those other females, even though Ginsburg’s mom is seen only in family photos.

But Leder shows little visual sense otherwise, something that would have come in handy in a movie that wants to sprawl out over several decades in the life of a character.

Then again, that sprawl couldn’t have been easy to deal with. If it pleases the court, I’d argue that there’s one big problem with this honorable attempt to tell us who Ruth Bader Ginsburg is: There’s too much material. RBG’s life is not a movie; it’s a miniseries.