“It is impossible to ever see an entire elephant from one place,” the wise and benevolent Eleanor Roosevelt tells a group of women in the extraordinarily moving “Warm Springs,” an HBO movie about the struggle of her husband to overcome his polio disability and eventually become president of the United States. “You have to walk around it.” But Franklin Delano Roosevelt could do no such thing. Stricken with polio at the age of 29 and confined to a wheelchair for most of his adult life, the great American statesman could see the elephant from wherever he sat. The compassion he learned from his handicap would become the defining element in a man whose abundant heart would soon shape the future of the free world, as its leader for 13 years.

It’s almost impossible to believe that little more a half century ago, a politician of Roosevelt’s stature could so effectively hide his debilitating illness from so many. In the years before he campaigned for the presidency, it turned out that he spent significant chunks of time seeking treatments for his condition at a broken-down spa in rural Georgia, where he’d heard of miracle cures. Instead of finding one there, he discovered through his experiences a different kind of cure – an emotional bond to those who suffered, and an understanding of people whose lives are altered by forces larger than themselves. In helping to turn Warm Springs into a polio rehabilitation center, Roosevelt focused his priorities on humanity in a way that would guide him through a Presidency in which humanity was challenged by unimaginable threats. The Roosevelt that emerges in “Warm Springs” is a man touched by greatness, who turned his greatest tragedy into his most powerful asset.

And there could be no actor better suited to the task than the great, gifted Kenneth Branagh, who has been far too absent from the screen in recent years. After bursting into the American consciousness as one of his generation’s foremost Shakespeare interpreters, Mr. Branagh faded into the relative obscurity of character roles. HBO has stayed loyal to his gifts, and he has repaid them with singular performances; he already earned an Emmy for his performance in the World War II drama “Conspiracy” and seems a likely winner again for his turn as Roosevelt in “Warm Springs.” It isn’t the cigarette holder or glasses that enables him to inhabit Roosevelt so completely, or even his superior skill at capturing that patrician voice. (“There’s a reason why they say a man runs for office,” he intones with a perfectly parceled twinge of regret upon realizing the effect of his health on his future political plans.) It’s his uncanny naturalism; having deftly played kings and princes, he warms quickly to the human side of leadership and imbues it with electricity and charm.

Director Joseph Sargent – a veteran master of the TV drama – filled out his cast with an uncommonly strong collection of character actors, among them the gifted Cynthia Nixon as Eleanor Roosevelt, Jane Alexander as the future president’s mother, and David Paymer as Louis Howe, a political operative trying to steer Roosevelt’s course amid all the tumult. The wondrous Kathy Bates turns up as Helena Mahony, who works with Roosevelt at Warm Springs to further develop the warm-water therapies that earned the place its eventual fame. And while Mr. Sargent brings little style or verve to the proceedings, he does step back far enough to allow this gifted cast an opportunity to shine. The scenes between Franklin and Eleanor grow from painful (in early scenes, when she learns of her husband’s extramarital activities) to touching, especially as their famous collaboration took hold.

“Warm Springs” ends at the start of Roosevelt’s epic political career; in 1928, when asked to introduce Al Smith to the Democratic National Convention, he makes it to the podium in such a way that demonstrates his determination to overcome his disease. It’s a powerful moment in a touching and evocative film that reminds us of Roosevelt’s resolve – and of how important it is for all of us to confront our weaknesses, and to transform them into strengths.

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Just when it desperately needed it, “Law & Order” got an adrenaline rush of talent and edge last week with the arrival of Michael Imperioli, who’s a four-week fill-in for the vastly inferior Jesse Martin. Hats off to Mr. Imerioli’s agent, who negotiated his client full status in the opening credits, and even got him an “opening walk” shot with his three co-stars – it’s like Mr. Martin never existed, which is just as well. I never liked his fey performance as Detective Ed Green (even his name was boring); the energy spark created by Mr. Imperioli last week was the theatrical equivalent of a first kiss on a warm spring night. Maybe Dick Wolf will figure out some way to gently dump Mr. Martin in favor of his new co-star, who has plenty of time to kill before shooting begins on the next season of “The Sopranos” in the year 2028.

“Warm Springs” airs April 30 at 8 p.m.