What DeSantis is doing is political, while his points seem valid. The disastrous Afghan exit may have emboldened US enemies, so by visiting the Ukraine now, Biden may be trying to repair the weakness seen by others around the world two years ago. The reaction from Putin to this new-look tough guy POTUS has not been very encouraging so far, so I hope that this does not all backfire.
As far as aid goes, remember that the war has only been on for one year. Before that Obama only sent non-lethal support. Trump sent missiles and other weapons, with the delivery of some of them delayed but only temporarily. Biden was slow to send weapons until the invasion has actually occured.