Immigration is essential to the future success of the United States. Without writing an economic theory paper, the short version is that the economic problems of the last twenty years has caused people to delay starting families, and the birth rate is dropping. Without immigration the US would not not have enough people to pay for things like social security and taxes to cover the existing national debt decades down the road.

One of the worst things longterm things (of many things) from the past several years has been the US making itself such an unappealing place for highly educated immigrants, like the recent attempt to block foreign students from studying in the US if classes where all online. We want those people to move here. There are also National Security implications, we want the smart people here.

It's a complex topic, and many countries have point systems that require certain valuable skills to be eligible. I don't think that's a bad idea, but anyone that thinks more people contributing to an economy is a bad thing doesn't know what they are talking about. Unfortunately, immigrants often get used as an easy scapegoat for problems they have very little impact on, like the taking your job argument (it's probably automation not immigrants).