The immigration problem is seen as huge in Europe, and also in the US. Therefore people choose candidates that are against more immigrations, or at least recognize this as a problem.
People are worried for economic reasons, integration-problems, violence, attack on women, terrorists. There are many reports, and people do not know who to trust, especially with the terrorists.
What would any of you think when 500 people from a far away country were placed near your house? You would experience it as a some kind of problem.
If we look back in history, we can see that a part of these (mostly male) immigrants are coming from Syria (some say only 25%). Syria is currently in a war with ISIS and Al Qaida. And at the same time Syria is under attack from "moderate rebels" that are supported by the US (continuing a policy against Syria). Also Kurds are fighting, and Turkey, sometimes against each other. And many more states.
It is a big mess. Most people do not see US meddling as a solution. Peace is usually achieved by NOT attacking people living in another country.
Tried to make it so simple that politicians can understand it ;-)