Can the Portent ability of a Diviner Wizard negate a critical hit?

Question

This question was inspired by the Question "Can Cutting Words cancel a critical hit?" According to a tweet by Jeremy Crawford, the Bardic inspiration ability cannot negate a critical hit. In fact he goes so far as to say that no penalty or modifier can do so:

Cutting Words can't nullify a critical hit—no bonus or penalty can (PH, 194). [Overrides a deleted 12/3 tweet]

This brings into question the Portent ability of a Diviner Wizard:

When you finish a long rest, roll two d20s and record the numbers rolled. You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

Can this ability, since it is replacing instead of modifying the roll, negate a critical hit?

Answer 1

Not as such, because the roll is never made.

Unlike the Bardic Inspiration, which modifies an existing roll (in this case a critical hit, the Portent die completely replaces the roll before it is made (PHB, p.116):

You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

It does not negate a critical hit, because if a critical hit is rolled, then the roll has already occurred.

The Portent ability requires the player of the Diviner Wizard to be on his or her toes. Rolling combat can often occur very quickly after intent is announced (sometimes without intent being announced at all in a very relaxed game), so if the Diviner wants to use their Portent ability, they must be ready to announce it in that very brief time.

Note that many DMs will be lenient in these cases, especially where not much time or warning was given, and some may even be willing to skip back a second, and say that the Diviner just "replaced the roll before it happened" regardless of how it actually occurred at the table.

Finally, note that since the Portent die replaces the die rolled, a player who rolls a 1 or a 20 on their Portent rolls has a very powerful ability indeed, since they now can grant a critical hit or a guaranteed miss at will until their next long rest.

Answer 2

No

You do not "negate" a critical hit with the Portent feature from the School of Divination.

You can however, replace the roll with your saved Portent roll. However, the critical would never have happened in this case since you have to announce that you are using the Portent before the other die is cast.