JB was down in Michigan Saturday for an event ahead of 4th of July ... and he was asked by CBS WH reporter Bo Erickson if he thought Richardson facing a one-month ban from competition due to a positive THC test was fair ... and Biden essentially said, sadly yes.

You can watch the clip yourself to see how he put it in his own words -- but the Prez didn't make any bones about it ... telling the press that everyone knows the rules going in, so it kinda is what it is on the punishment end. He did leave room for debate, however.

Check it out ... Joe says whether the weed rule should stay intact or not is an entirely different discussion -- but under the current guidelines, he suggests the punishment fits the crime. With that said, he did give Richardson props ... saying he was proud at how she responded.

Sha'Carri did an interview shortly after the news broke that she'd been temporarily DQ'd ... telling Savannah Guthrie she ingested marijuana recently, this after learning her biological mother had died and learning about it at a presser. Sha'Carri owned up to the mistake with her chin high -- but also seemed to indicate that the so-called "rules" were draconian.