Among you. In your midst.
If we ask the question, In what way could the Kingdom of God, be in the midst of, or among the Jews, including the Pharisees who were trying to trap him, it might be fitting to ask, what is the kingdom of God.
If the Kingdom of God is a heavenly kingdom, or rulership (government), as the scriptures evidently show, then it makes sense that Jesus was there saying, "Hey guys..."
Just kidding..
"Don't let anyone mislead you by saying, 'This (someone other than Christ Jesus) is the one coming to restore things'. Or 'Look! This one in the desert is he.' because the ruler - the true Messiah who will restore all things - the one designated king and ruler, in the kingdom of God is here among you, in the midst of you. I - the one - am here... among you."
In other words, Jesus, the designated king and representative of God's kingdom was among the people, in their midst. In that way, the kingdom of God was among them.
It makes sense that the true Messiah would forewarn the people, to be alert to the fact that persons would reject him, and look to a future leader that would claim to be the one to restore, or finish all things.... and we see that that has indeed occurred.