1. Every temporally contingent thing has a sustaining cause. (Premise)
2. If there is no First Cause, then there is an infinite regress of temporally contingent sustaining causes. (Premise)
3. There cannot be an infinite regress of sustaining causes. (Premise)
4. Therefore, a First Cause exists. (From 1 - 4)
5. Every existing thing is either omnipotent or non-omnipotent. (Definition)
6. Whatever is non-omnipotent can be generated. (Premise)
7. A First Cause cannot be generated. (Premise)
8. Therefore, the First Cause is omnipotent.
An omnipotent First Cause, as the Angelic Doctor muses, "everyone understands to be God."
Notice that the second half of the argument is almost identical to the Modal Third Way (MTW) that I defend on this blog. The first half of this version of the TCA, on the other hand, is more traditional.
As believers we often get the question: why does the First Cause have to be God?
This is a good and fair question, but it is also one that can be answered quickly with success. (5) - (8) show that the First Cause must have omnipotence, an exclusively God-like characteristic.