Do both targets of Green-Flame Blade (gained by the Arcana Domain) benefit from Potent Spellcasting?

Question

Clerics with the Arcana domain get special powers:

ARCANE INITIATE
When you choose this domain at 1st level, you gain proficiency in the Arcana skill, and you gain two cantrips of your choice from the wizard spell list. For you, these cantrips count as cleric cantrips.

POTENT SPELLCASTING
Starting at 8th level, you add your Wisdom modifier to the damage you deal with any cleric cantrip.

If I pick Green-Flame Blade (Sword Coast Adeventurer's Guide) at level 1, do I get to add my Wisdom modifier against both opponents?

Answer 1

The answer is sometimes. Green-Flame Blade says:

On a hit, the target suffers the attack's normal effects, and green fire leaps from the target to a different creature of your choice that you can see within 5 feet of it.

You make an attack and resolve it normally, then it deals fire damage to an adjacent target. In this case you would only deal the extra damage to the second target because that is the only damage caused directly by the spell.

This changes however when you hit level 5

At 5th level, the melee attack deals an extra 1d8 fire damage to the target, and the fire damage to the second creature increases to 1d8 + your spell casting ability modifier.

At this point you would apply the extra damage to both targets, because the spell is actually causing the extra fire damage.