Answer: The word "muscle" there can be seen as a figure of speech. It doesn't literally mean the law has physical muscles but rather implies authority or ability to do something better.
Step-by-step explanation:
The word "muscle" there can be seen as a figure of speech. It doesn't literally mean the law has physical muscles but rather implies authority or ability to do something better. In the paragraph, the word "which gave him legal muscle to do whatever he wanted" means that the law gave him the right to carry out with what he wanted to do which was enforcing the city laws.