Overall these levels aren't too difficult, the only area where I had the most trouble was the final boss.
The President works the best against him as with the machine gun he can land the most amount of hits the quickest. Try to stay constantly moving back and forth across the room as he will attempt to trap you often with the blue fire; on that topic, if you shoot the orbs before they hit the ground, nothing will happen. I've found that the easiest way to take them out was to do a single jump as they are coming towards the ground then shooting them.
Don't double jump too often as arrows are shot across the higher points of the room. You will probably get screwed over a few times on spawns (i.e. being trapped in a corner and getting spiked / blue flamed), but it shouldn't take more than a few attempts to bring him down.