Build up of bacteria at night means that if you eat in the morning before brushing there will be more bacteria to break down the food into acid which will break down your teeth.
Ideal is to brush first but also brush after each meal*
*as long as the acidity in your mouth is 5.5pH or less your teeth are being broken down by the acid (which means that brushing would be scrubing them with acid and making it worse) in which case you should wait until your spit (which is a buffer solution) returns your pH to normal. Since most foods are acidic the recommendation is to wait 30 mnutes after eating and then brush. Or you can eat suger free gum right after a meal, this will trick your brain to produce more spit which will return the normal pH faster.
My personal system is like so:
Wake up
Use dental jet floss (water floss)
Brush teeth
After any foods eaten chew gum for 10-30 minutes
Floss
Dental jet (if at home)
If I’m at home and have 30 minutes to wait between mouthwash and brushing then I use mouthwash, wait 30 min then brush, if not then just brushing and if I’m not at home then just mouthwash.