If Charging Tuskodon has trample damage to assign to a player, that damage is assigned based on its actual power and is doubled only as it’s dealt. For example, if Charging Tuskodon is blocked by a 3/3 creature, the attacking player can assign 1 damage to the defending player and then Charging Tuskodon deals 2 damage to that player.

The doubled damage Charging Tuskodon deals is still combat damage.