Here is the logic of Josh McDowell’s version of the Trilemma argument found in Chapter 7 of Evidence that Demands a Verdict and Chapter 2 of More Than a Carpenter:

1. Jesus claimed to be God.

2. If Jesus claimed to be God, and Jesus was not God, and Jesus knew that he was not God, then Jesus was a liar.

3. If Jesus claimed to be God, and Jesus was not God, and Jesus did not know that he was not God, then Jesus was mentally ill.

Therefore:

4. Either Jesus was a liar, or Jesus was mentally ill, or Jesus was God.

5. It is not the case that Jesus was a liar.

6. It is not the case that Jesus was mentally ill.

Therefore:

7. Jesus was God.

As formulated here, this is a deductively valid argument (both inferences are valid).