Steve Bannon's calling out the elephant in the room where Mark Cuban's considering a run for the presidency as a Republican ... by labeling him a donkey.
We got the Breitbart exec Monday in D.C. and asked if Mark would be taken seriously as a Republican if he were to run against Trump in 2020 ... his answer's brief, but telling.
As we reported ... the Dallas Mavericks owner told Harvey Levin on "OBJECTified" Sunday night that he'd run against 45 under the umbrella of the GOP ... if he decides to.
Doesn't look like Bannon would be in his corner on that front ... cross the aisle, maybe?