Jonathan Drake: "They lost faith in the face of such an enemy and failed to drive them out."
Read the Scripture carefully:
19 The Lord was with the men of Judah. They took possession of the hill country, but they were unable to drive the people from the plains, because they had chariots fitted with iron. Judges 1:19 New International Version
If the Lord was with them then that means that they had faith at that point in time, thus he should have accomplished the deed. There is nothing in this scripture that says they lost faith at that particular moment.