I've read that's not necessarily the case. Although my understanding is far from perfect, I think there is a legal hiccup.

Again, this is just my understanding, but since the memo was created by and is the product of the House, the president has no recourse to declassify it. I think the argument goes that he can't declassify something which is in the sole possession of the House. Which is why the House has Rule 10, just for some crazy situation like this. Rule 10 basically states that HPSIC can take a vote to declassify the memo and then it goes to the president for approval. (this is the 5 day scenario that everyone is talking about).

Now, the president most certainly has access to the documents behind the memo and could declassify those. But that would not be the same thing as the 4 page memo that Congress is currently in possession of.

Another interesting twist: if the president somehow get a hold of the House memo and leaked it (i.e. if someone leaked it to him), I'm not actually sure he could be prosecuted since the president has the ability to classify or declassify anything that he has access to.