This is a good request. It is very hard to describe the middle class without defining what the middle class is. Moreover, since this definition changes from time to time, it is hard to define. Then, there is also the problem of regional differences. In other words, middle class in New York is different from middle class in Scranton, PA. I will attach a good article on this topic in the first resource link.
With this stated, let me give you a few characteristics that most people agree with.
First, the middle class is not doing well in America. The middle class is getting squeezed. Prices are rising, but real wages are not climbing. Economists call this stagflation.
Second, the middle class is getting smaller. There are more people in poverty now and the rich are getting richer. The country is becoming increasingly a nation of haves and have nots.
Third, a lot of the jobs that would make people in the range middle class have been outsourced to other countries.