Clint Eastwood's RNC Speech -- Bumbles Through Invisible Obama Schtick

Clint Eastwood brought down the partisan crowd at the RNC by stumbling through an 11-minute bit last night that was supposed to be painfully hysterical ... but might have been just painful.

The legendary actor/director got on stage and addressed an empty stool next to him, saying ... "I've got Mr. Obama sitting here. I just was gonna ask him a couple questions."

During the schtick 82-year-old Clint seemed confused at times as he critiqued the President's 4 years in office ... and set up punchlines like, "What do you want me to tell Romney? I can't tell him to do that. He can't do that to himself."

President Obama responded to the invisible routine this morning by tweeting a pic of the back of his chair with the message, "This seat's taken."

No doubt, landing an icon like Eastwood to warm up the crowd for Mitt Romney was a coup for the GOP -- but still, we gotta ask ...