Some of the memes:
If you don't understand the old German letters I typed it out using my American keyboard so there are no umlauts or eszets, but this will allow you to cut and paste into google translate and make your own decision. You can see that some of the words are not correct, or incorrectly translated by google within the context, but the main point is there.
"Eine einzige Gefahr konnte es gegen diese Entwicklung geben: Wenn der Gegner das Prinzip erkannte, Klarheit ueber diese Gedanken erhielt und jeden Widerstand vermied. Oder wenn er mit letzer Brutalitaet am ersten Tag den ersten Keim der neuen Sammlung vernichtete." -Hitler, 1933
Taking into consideration how translation works, this quote is genuine.
I saw the first one on facebook, and someone in the comments said it was untrue and that it fell under the category of "fake news." Another commenter pointed out that it's a translation and subject to the interpretation of the translator, then gave the quote in German (still all in the comments of facebook). I've studied German and traveled there several times and from the quote I saw (in the facebook comment) the translation is good. As the original poster explained, the word nucleus was not a word Hitler used but it was accurate. A good translation conveys the meaning behind the words as well as the words themselves, and this translator thought smashing the nucleus captured the meaning of Hitler's words.
I found some good information on a blog, Z ZONE (https://zuriz.wordpress.com/2013/10/06/smashing-the-nucleus/), and it turns out the quote has been thrown around for decades. The blog attributes it to a 1976 play and points out that a supposed original version (in German) is actually translated from English to German and bogus. The comments on the blog have a wealth of information and better translations than mine, but the important take-away is that this IS a quote from Hitler. It's interesting to note that the blog post is from 2013 and its discussion on liberal strategy is not related to the 2016 US election.
The speech the quote is taken from was given at the 1933 Reichsparteitag conference, later published in a 1934 Nazi book. The book is archived at http://archive.org/stream/Die-Reden-Hitlers-am-Reichsparteitag-1933/DieRedenHitlersAmReichsparteitag1933193427Doppels.ScanFraktur#page/n21/mode/1up. The last paragraph at the bottom of page 41 is the quote in question, here's a screenshot:
If you don't understand the old German letters I typed it out using my American keyboard so there are no umlauts or eszets, but this will allow you to cut and paste into google translate and make your own decision. You can see that some of the words are not correct, or incorrectly translated by google within the context, but the main point is there.
"Eine einzige Gefahr konnte es gegen diese Entwicklung geben: Wenn der Gegner das Prinzip erkannte, Klarheit ueber diese Gedanken erhielt und jeden Widerstand vermied. Oder wenn er mit letzer Brutalitaet am ersten Tag den ersten Keim der neuen Sammlung vernichtete." -Hitler, 1933
Taking into consideration how translation works, this quote is genuine.