People tended to react with amazement at Thursday's now-viral footage of President Obama singing a few bars of Al Green's "Let's Stay Together," but our painstaking research reveals that breaking into song is actually something of an ace-in-the-hole move for the president. Obama spoke Thursday at a fundraiser and after announcing that the Rev. Al Green was attending, he sang a couple of lyrics, and, by the hammer of Thor, he sounded kind of good! It wasn't Clinton giving his all on the saxophone on Arsenio good, but it was pretty suave. So herein, an examination of Barack Obama's greatest hits, along with our brief analyses and highly scientific letter grade rankings. 

1. Barack Obama - "Walk on By." At a campaign rally, Obama notes that Dionne Warwick is "in the house." and says when he and his friends were young and wanted to "like, really be smooth ... you slip in the Dionne Warwick." before breaking out into 8 seconds of "Walk on By." The affair is actually almost identical to the circumstances surrounding his Al Green moment. We'll give points for his rich baritone, but subtract some for his doofy hand-movements. Our grade: B+

2. Barack Obama - "Chain of Fools." Here we are again. Campaign event. 2008. Obama thanks Aretha Franklin. Then spontaneously (well, probably not spontaneously, by now he knows the magical powers this move has) starts singing "Chain of Fools." Points for his soulful rasp (probably campaign exhaustion) but deductions for his questionable grasp of what key he was in and for curtailing it so soon! Our Grade: B.

3. Barack Obama - "Happy Birthday." Okay, okay, we're not saying Barack Obama is the most prolific recording artist out there. It's like when Britney Spears put out a greatest hits album in 2004. There's just wasn't that much material to draw on so she had to fill the track list out with random stuff like "Born to Make You Happy." This is Barack Obama's "Born to Make You Happy." He's at a campaign event in Philadelphia and sings to some lucky duck named Timmy who turned 13. It's not very good. He is just clearly not focusing, he probably can't hear himself without one of those fancy flesh colored earpieces. Basically, he's a pitchy mess, and oof, the high note is just not there, Mr. President. Our grade: D-

4. Barack Obama - "Lift Every Voice and Sing" (featuring Smokey Robinson, Jennifer Hudson, Bob Dylan, and a dozen other famous people.) Obama got some heavy lifters here to help him out with this one. He's at a White House celebration of African-American history month and he and the rest of the crew ended the event with "Lift Every Voice and Sing." We wouldn't really count this because it's more of an ensemble number, except you can really distinctly hear him when the group comes in because he's clearly holding his microphone much too close to his face, and then after a few seconds, someone off screen clearly instructs him to move it away. We give many points for the strong vocals surrounding him. (It's similar to the way Katy Perry uses her backup singers.) But deductions for the main man's bad microphone technique. Our Grade: C. 

5. Barack Obama - "Let's Stay Together." You've seen it by now. And there's a reason this one went viral. The soul. The effortless switching of vocal registers. The cool squint. This is unquestionably the greatest of his greatest hits. We just wish he'd gone on longer. Our Grade: A.