Since the game is really hard here are a list of cheat codes you can use in campaign to make it way easier:

To open up the cheat console thing press the tilde key ( ~ ) and then copy and paste these commands in,

Fly: lets you fly around
Ghost: lets you go through walls (works well with fly)
Walk: disables ghost and fly
AllWeapons: spawns every weapon (you can only hold one weapon at a time besides modifications)
Loaded: does the same thing as AllWeapons but you also get full ammo on all weapons
Fierfek: get full ammo on all weapons
SmiteEvil: kill all enemies (doesn't kill enemies spawned after the command)
Invisible 1: makes you invisible to enemies
Invisible 0: makes you not invisible to enemies
BehindView 1: enables 3rd person (difficult to aim)
Behindview 0: disables 3rd person

Lamasu: unlocks all levels but kinda ruins the fun
Darman: skips the current level but also kinda ruins the fun
TheMatulaakLives: enables god mode and is actually really fun

I hope that this helps you beat the campaign