Marco Rubio -- I'm No Aaron Rodgers ... Fires a Duck, Kid Goes Down (VIDEO)

Republican presidential candidate Marco Rubio is losing ground in the polls -- and this video won't help ... not with the diehard football fans.

Rubio was tossing the pigskin with some kids in Iowa -- where every other candidate is hanging this week -- and let's just say he needs to work on his spiral ... or get Odell Beckham Jr. as his running mate.

He made it near impossible for the poor kid going out for the pass -- although, in Rubio's defense ... it did hit him in the hands. Awkwardly.