Can War Priest and Precision Attack both be used on the same attack?

Question

I am playing a level 4 character: Cleric, War Domain (1) and Fighter Battle Master (3).

The War Domain's War Priest feature is described as follows:

From 1st level, your god delivers bolts of inspiration to you while you are engaged in battle. When you use the Attack action, you can make one weapon attack as a bonus action. You can use this feature a number of times equal to your Wisdom modifier (a minimum of once). You regain all expended uses when you finish a long rest.

The description of the Battle Master's Precision Attack feature:

When you make a weapon attack roll against a creature, you can expend one superiority to add to the roll. You can use this maneuver before or after making the attack roll, but before any effects of the attack are applied.

The question: Can both features be used in the same attack, or must they be used on separate independent attacks?

Answer 1

Yes, you can stack those abilities

As you quoted, the use of the War Priest is a limited resource that also requires the use of a Bonus Action. This means that you are limited in how many times you can use it (based on your Wisdom modifier) and also that it requires your Bonus Action (You only get one bonus action per turn).

The Precision Attack uses your limited resource of Superiority Die, but it does not complete with your Bonus Action usage or anything else.

In your case, if you use an Attack action you can use your Bonus Action to make another weapon attack. If you had enough Superiority Dice available, you could use them on both attacks.

Answer 2

Yes, you can use both in the same turn.

That said, the two abilities wouldn't exactly apply to "one attack", since they have slightly different triggers and work in different ways.

The War Priest feature lets you make one weapon attack as a bonus action if you use your action to do the Attack action.

In contrast, the Precision Attack maneuver applies to any single attack roll. (See this thread for the distinction between an attack (or attack roll) and the Attack action.) It lets you expend a superiority die to add the amount on the superiority die to your to-hit roll for one attack roll. You could do this on any of the attacks you get on your Attack action (you'd get more attacks per Attack action at higher levels as a Fighter) or on the single bonus action attack you get through the War Priest feature.

The two features are limited by different things: War Priest by your Wisdom modifier, Precision Attack by your number of superiority dice.