The "Close the Gate" political cartoon was created during 1919. This was the era of the Red Scare, where Americans feared the Soviet Union and communism infiltrating American society. With this in mind, you can better understand the cartoon.
If you look, on the suitcase there is says "undesirables." This shows how the author sees the immigrants coming in as a detriment to society.
On the gate, it says "Immigration restrictions." If this gate is closed, it will effectively limit who is coming into the United States. These restrictions will help to ensure that foreigners won't spread their ideas/bad influences into American society.
Lastly, his head is shown as a bomb with a fuse light. This is symbolic, as it is saying that it is only a matter of time before this person does something bad.
