The first sentence in your introduction is your hook:
Semi-automatic rifles such as the AR-15 have become the weapon of choice for mass shooters. They have been banned before, yet countless gun owners are determined it will never happen again.
The last sentence in your introduction is your statement:
Therefore, the production, sale, and possession of assault weapons for private citizens should be banned in the U.S.
What can you write to connect these two?
-> Give some background information about the problem.
-> Use linking words to connect your ideas and sentences