My Cleric has the Warcaster feat, a mace in his right hand, and a shield in his left. He casts inflict wounds, which requires a touch attack to be executed against an opposing enemy, a goblin for instance.
If the cleric uses his mace as a means to touch the creature, would this function as a touch attack? Would this deal mace damage in addition to the Inflict wounds? Why or why not?
All the Warcaster feat does is negates the need to have one hand free to cast the Somatic component of spells, so long as your hands are occupied by either weapons and/or a shield.
It doesn't allow you to cast spells through a weapon.
Inflict Wounds allows you to make a melee spell attack not a melee weapon attack. As such, unless otherwise stated in the spell's description, only the spell damage is inflicted, not the weapon damage.
While there is no "touch attack" in 5e D&D, let's walk through how Inflict Wounds works.
Inflict Wounds has both Verbal and Somatic components. Somatic components require:
Grey Mens Brooks 3 Punch Black Primer Launch Lime HXHqfwdA free use of at least one hand to perform these gestures. (p. 203 PHB).
The simplest thing to do in the usual case is to drop or sheathe the mace and cast Inflict Wounds, per the spell. Dropping or sheathing the mace costs you neither an action nor a bonus action. Refer to page 190 of the PHB and "Interacting with Objects around you" as well as "Other activities on your turn."
Lace Breathable Sports Red Sneakers up Athletic Sikye Men's Casual Outdoor Running Shoes Canvas Fashion XzgRqEYour turn can include a variety of flourishes that require neither your Action nor your Move.
Since you could draw or sheathe a weapon as one such interaction, dropping or sheathing your mace leaves your hand free to cast that spell.
You can't cast the spell through your mace. You need a free hand ...unless you have the Warcaster feat. In that case, you can cast the spell with the mace in your hand.
You can perform the somatic components of spells even when you have weapons or a shield in one or both hands.
Because you have the feat, you can cast the spell and your Inflict Wounds does the damage ... if you score a hit. That spells requires that you roll for a hit. (See page 205 of the PHB). It is described as a melee spell attack on page 253 of the PHB.
On a hit, the target takes 3d10 necrotic damage.