I agree with Karin’s answer. There is really no one answer to this question. A lot depends upon your goal(s) in training. For example, if you are working on maximum strength development, then strength training first (after conducting a proper warm-up of course) is the best way to achieve this goal. As Karin correctly identifies, if my goal is muscular endurance instead, then performing my cardio workout first should not really present a problem in my training since I am not using maximum resistance in my resistance training, and I actually want to encourage my muscles to adapt to having to work while being somewhat fatigued.
That being said, I’m a firm believer in mixing it up! So, oftentimes, despite my own or my clients training goal, I will sometimes conduct cardio first and resistance second or vice versa. I think this helps me present a different challenge to the body and in truth mimics more closely what might occur in the real world (i.e. my client doesn’t always get to choose to perform a strength movement when they’re fully rested…).
I hope this helps.