Does the Flame Blade spell count as a melee weapon that can be used with the paladin's Divine Smite feature?

Question

With the release of the new Mordenkainen Presents: Monsters of the Multiverse, the revamped Fire Genasi trait "Reach to the Blaze" now allows the race access to the flame blade spell:

[...] Starting at 5th level, you can also cast the flame blade spell with this trait, without a material component. [...]

This made me think, if flame blade can be used with the paladin's Divine Smite feature, casting flame blade at 5th level with Divine Smite using a 5th-level spell slot will result in 4d6 fire damage and at least 5d8 radiant damage.

Does flame blade count as a melee weapon that can be used with Divine Smite?

Answer 1

No

Generally, flame blade is not considered a weapon and so doesn't work with spells and features which require one, such as green flame blade or opportunity attacks.

For Divine Smite though there's an even more clear cut issue. Flame blade has you make a spell attack (emphasis added):

You can use your action to make a melee spell attack with the fiery blade.

and Divine Smite requires a weapon attack:

Starting at 2nd level, when you hit a creature with a melee weapon attack, you can expend one spell slot to deal radiant damage to the target, in addition to the weapon’s damage.

Thus this doesn't work without a DM overriding it (which is quite possible for flame blade).