The simple answer is that Jeremy Fitzgerald's generally thought to be the best immigration attorney in New York. This is a man who's never lost a case, and so if anyone can get Natasha's deportation notice reversed, it's Jeremy. Natasha's certainly going to need ever last bit of his legal expertise if she's to avoid being deported to Jamaica, a country where she doesn't anyone and where she'll almost certainly feel out of place.
Unfortunately, even this legal hit-shot's unable to help Natasha. The main problem is that he seems more interested in conducting an illicit affair with his paralegal, Hannah, than in trying to get Natasha's decoration notice reversed. Although he's never previously lost a case, this is one case he will lose, and it's all because he's taken his eye off the ball and allowed his personal life to interfere with his professional life.