What is the name of this grammatical phenomenon?

Question

I have observed that many native English speakers (esp. American English, in my experience) tend, within the same sentence, to start a new clause whose subject is an element of the previous clause. Here is an example:

That is what fascinated me about programming—is that it changes the way you think about the world.

In this sentence, "what fascinated me about programming" is used as an object in the first clause, but then gets reused as the subject of the second clause.

Other examples:

• This is something we talk about a lot—is the size of the community is substantially smaller than the React community [...]

  (source)

• This is what I think went wrong is what Trump did very effectively is tap the angst and the anger and the hurt and the pain that millions of working-class people are feeling.

  (source)

I have only noticed this phenomenon in spoken English, as opposed to written English. What are its name and origins?

Note: I'm aware of the double copula (a.k.a. "double is"); this is related, but different.

Answer 1

As a figure of speech, this is called anacoluthon—when you break the grammatical structure of a sentence and begin a new construction or a fragment of a construction. This Greek word means "that which does not follow". The term is less used outside of a literary context, but it is the same phaenomenon.

It is commonly indicated in writing by a dash (although not all dashes indicate an anacoluthon: they can also be used for parenthesis, which means that the grammar is only temporarily interrupted, to be resumed afterwards).

I have to say, though, that your example strikes me as ugly. A good anacoluthon is used for rhetorical effect; when that is not the case, it is often simply considered an error. As to when it is considered an error and when it's not, that is very difficult to define.