Dr. Craig is a liar.

[Time Traveler]

That does not make the argument invalid. 

My understanding of assigning probability to an inductive argument is looking at the relationship of the probability of the premises and the conclusion. 

1. Everything that begins to exist has a cause
2. The universe began to exist
3. The universe has a cause (and we can assign some description to the cause)

Assign a probability to each premise and the conclusion's probability cannot be lower than the lowest of the premises. It can be higher. There are only two of them so it is not all that complex. Since each premise is reasoned out and defeaters for them seem to be at least less plausible, the conclusion that the universe has a timeless, powerful, transcendent cause seems to also be > 50%. 

I am not saying this is 100% proof for God. Only saying that it supports the concept of the God of the Bible.

1. Everything that begins to exist has a cause
2. The universe began to exist
3. The universe has a cause (and we can assign some description to the cause)
4. The multiverse has always existed and is the cause of the universe. (Description assigned.)

The conclusion that the universe came from a multiverse seems to be > 50%.

I am not saying this is 100% proof of the multiverse. Only saying that it supports many scientific models which theorize a Multiverse.

Syllogisms work for scientific theories too. The difference is, scientists work to test their theories empirically, theists don't.