There is a previous thread that asked this, but it wasn't answered as explicitly as I would like.
I have 2 Harness the Storms on the battlefield, 1 Lightning Bolt in hand, and 1 Lightning Bolt in the graveyard. If I cast the Lightning Bolt in hand, both Harness the Storm trigger and target the one in my graveyard. If I cast the graveyard Lightning Bolt from the top trigger, can I still cast it again with the second trigger or is it a new object since it changed zones?
In general, if the same object is targeted by two or more spells and/or abilities and one of them moves that object elsewhere (directly or indirectly), that object will be an illegal target for any other spell or ability that targeted that object, even if the object then returns to its former zone (C.R. 608.2b, 400.7). And in general, a spell with targets that are all illegal will fail to resolve (C.R. 608.2b).
Thus, in general, if you target the same card with two or more Harness the Storm abilities and cast that card with one of them, that card will be an illegal target for any other spell or ability that targeted it, including the other Harness the Storm abilities.
In addition to Harness the Storm, other examples include—
I have 2 Harness the Storms on the battlefield, 1 Lightning Bolt in hand, and 1 Lightning Bolt in the graveyard. If I cast the Lightning Bolt in hand, both Harness the Storm trigger and target the one in my graveyard. If I cast the graveyard Lightning Bolt from the top trigger, can I still cast it again with the second trigger or is it a new object since it changed zones?
Thanks.
Thus, in general, if you target the same card with two or more Harness the Storm abilities and cast that card with one of them, that card will be an illegal target for any other spell or ability that targeted it, including the other Harness the Storm abilities.
In addition to Harness the Storm, other examples include—
EDIT (Nov. 18, 2021): Edited to add "in general" in view of mutate rules.