There is a Robert Frost poem called “Escapist – Never” which provides a frequent refrain in Greg Barker’s deeply admiring but drawn-out biopic of Brazilian diplomat and U.N. leading light Sergio Vieira de Mello. “It is the future that creates his present,” runs the penultimate line, and the handsome, heroic, charismatic de Mello (played with persuasive charm by Wagner Moura) certainly does seem like a man whose present was shaped by the future — specifically by the better, brighter, freer global future he believed the U.N. could be instrumental in achieving and that he personally could help midwife into being.

Such noble intentions and such impact on world affairs does render understandable Barker’s rather starry-eyed approach, but in its unnecessary length and sentimental emphasis on the man’s romantic life, “Sergio” more often, intentionally and otherwise, evokes the “interminable chain of longing” of the poem’s celebrated last line.

“Sergio” begins with a re-creation of an actual to-camera piece that de Mello, then U.N. High Commissioner for Human Rights, recorded to welcome and inspire new recruits to the organization. Though it’s filmed in an office from behind a desk, de Mello ends on an exhortation to value field work above all else, neatly cuing up the nesting-table series of flashbacks and flash-forwards detailing his own time on the ground in Cambodia, East Timor, Indonesia and, finally, Iraq.

First, we spin forward to the 2003 bombing of the U.N. headquarters in Baghdad, which was ordered by terrorist leader Abu Musab al-Zarqawi and which claimed at least 22 lives and wounded over 100 people, and here provides a loose framing device. De Mello and close associate Gil Loescher (Brian F. O’Byrne), both critically wounded, were trapped under tons of rubble in the blast, and so in between detailing the surprisingly under-resourced rescue attempts, which mostly boiled down to two lone American soldiers (played by Garret Dillahunt and Will Dalton) attempting to move precarious fallen masonry by hand, screenwriter Craig Borten imagines a borderline delirious de Mello reliving moments of significance from his storied life. Chief among these reminiscences is the tale of his romance with Carolina Larriera (Ana de Armas, reuniting with Moura after “Wasp Network”), an Argentinian U.N. economic adviser whom the father-of-two met while brokering a peace deal between the rebels and the Indonesian government in East Timor and whom Netfliz informs viewers was ultimately recognized by Brazil as his civil spouse.

In Adrian Teijido’s calm, throughful photography (it’s a refreshing choice to not go the shaky handheld docudrama route), de Armas and Moura make an attractive couple, and de Armas is able to imbue Carolina — whose role seems just a little wispy on the page — with an intelligence and will that makes it clear that she was more than just de Mello’s romantic foil. But Barker’s emphasis on this love story at the expense of a deeper exploration of the exceptional talents that earned de Mello his reputation for feats of diplmatic wizardry in highly fraught situations where others had tried and failed, also has a curiously flattening effect.

Although the relationship with Larriera was doubtless crucially important to de Mello, it was not the thing that made him extraordinary in the eyes of the world. And so the hesitant courtship, the smouldering looks, and the romancing, including a tasteful but unnecessarily lengthy sex scene over which Fernando Velázquez’ otherwise rather generic political-thriller score crescendos like it’s high drama, all feel like a distraction from the more thorny and politically provocative side of de Mello’s story. That’s especially irksome given that the scenes of geopolitical debate, diplomatic argument and even ego clash between de Mello and the world-wearily witty Loescher (with Moura having fully as much chemistry with a terrifically wry O’Byrne as he does with de Armas) are actually where the film crackles to life.

Barker comes from a documentary background and already told de Mello’s life story in a 2009 nonfiction film, also called “Sergio.” So perhaps it’s understandable that given the license of fictionalization, Barker would try to explore avenues that his documentary could not easily show: the workings of de Mello’s mind; the memories and regrets that perhaps floated through his consciousness during those painful, lonely hours trapped in the shifting rubble. But this sentimental approach glosses over much of the potential drama that is set up only to dissipate: de Mello’s prickly relationship with U.S. Envoy Paul Bremer (Bradley Whitford); his association, criticized by Loescher, with war criminals and terrorists if he believed it could achieve his ends; and his fateful decision to send the U.S. Army guards away from the U.N. office in Baghdad in 2003. Sergio Vieira de Mello was, by all accounts, not a man who let fear of making the wrong decision stop him from acting decisively, and it’s a shame that the soft-edged romantic prevarications of “Sergio” prevent the film from embodying that same dynamism.