It's been a good month on the charts for soul legends: First, reports surfaced that Etta James posted a 378 percent sales increase in the week after her death, and now comes word that President Obama's brief rendition of Al Green's 'Let's Stay Together' at a recent fundraiser has prompted a 490 percent spike in purchases of the classic track.

The YouTube video of the event, which has been viewed more than 4 million times, sparked a viral craze that included its own ringtone and served as a fitting tribute for Green, whose most recent release, 2008's 'Lay It Down,' debuted in the top 10 of Billboard's album chart.

"Those guys didn't think I would do it," Obama joked after singing, pointing to his staff. "I told you I was going to do it." Referencing the Apollo Theater's infamous hook-wielding Sandman Sims, Obama quipped, "The Sandman did not come out. Don't worry, Rev -- I cannot sing like you, but I just wanted to show my appreciation."

Watch President Obama Sing Al Green's 'Let's Stay Together'