How do I handle a catfrontation?

I adopted a beautiful cat that was orphaned by TS Fay, but my beautiful other cat is none too happy about it. I tried keeping them-separated and letting them get acquainted through smell, but they would just howl at the door, so i let them meet. Original cat has been very defensive and on edge ever since.

What do I do? There’s been hissing, horking, and one cat isn’t eating as much. I’ve only had this new cat for 2 days. Do I have anything to worry about it? Is this normal? Will it subside? Thank you.