Partitioned Table Index Column Order

All,

I'm on PostgreSQL 13 and have a partitioned table with a primary key.

create table t( a integer, b integer, c varchar, d .. ) partitioned by
range( a );

As a best practice is it better to create the primary key starting or
ending with the partition column?

e.g.
1) t_pkey primary key (a, b, c)

or

2) t_pkey primary key (b, c, a)

Neither the PostgreSQL documentation nor Google have an answer - at least
as far as I could find. I see examples in the Postgres documentation that
use 2) but no explanation of why that choice was made.

Does it even make a difference?

Thoughts?

--
Rumpi Gravenstein