Robin Thicke -- I'd Love to Do a Duet with President Obama!

Count Robin Thicke among those who think President Barack Obama killed it when he sung Al Green's "Let's Stay Together" ... in fact, Robin told our photog last night he'd jump at the chance to sing alongside the Prez.

Obama dropped a few notes of the classic song (see below) during an event Thursday night. TMZ spoke with Al Green, who was in attendance, and he called Obama's singing "terrific."

Al Sharpton took it a step further yesterday, when he told our photog he thought Barack's singing would be good for re-election.

Maybe Al could be his running mate.