I'm a huge fan of both the book and the musical, but I picked this up from someone on my f-list who knew nothing of Les Miserables but still enjoyed it. The song is the closing number of the first act of the show, in which a) Valjean, the tragic hero of the story, decides to flee to England; b) Marius, the romantic hero of the story, decides to fight alongside the revolutionaries since he cannot stay with Valjean's [adopted] daughter Cosette, his love interest; c) Eponine, in love with Marius, decides to fight alongside the revolutionaries since he's there even though he doesn't love her; d) Enjolras, the revolutionary leader, decides to revolt; e) Javert, the secret policeman, decides to pass himself off as a revolutionary; f) Eponine's parents, the disreputable Thenardiers, decide to wait until everyone is dead and rob the corpses and g) everyone sings about it, summing up the first 80% of the novel in three and a half minutes. Les Miserables is full of good songs, but this is probably the best of them.
Les Miserables is much better known than the abortive 5 June 1832 revolution which it chronicles. Historians of mathematics may derive some satisfaction from the fact that, though it was the death of General Lamarque which caused the outbreak of revolt, tension had already been raised by the murky death of the revolutionary mathematician Évariste Galois a few days earlier.
Because it's a stage show which hasn't been filmed, it's surprisingly difficult to find YouTube videos which give the true feeling of watching it as it should be (and don't have the appalling Michael Ball). This is the quasi-canonical version from the Anniversary concert, but of course it's just people singing into microphones (even if appropriately costumed, and including the brilliant Lea Salonga as Eponine, though sadly also the said M Ball). The Lego version is surprisingly true to the spirit of the stage show. You might also want to check out two German versions here and here.
The vid linking the Obama campaign to the song is uplifting and hugely enjoyable, but I do wish they had picked a literary parallel where more of the characters avoid untimely deaths. As I recall, only Marius, Cosette and the Thenardiers survive to the end of stage the show (and in the book I think Madame Thenardier snuffs it too). Let us hope for a better survival ratio among the Obama campaign, whatever the result.