Donald Trump recently lost his lead in the polls to Ben Carson, so now he's employing Carson's tactics to catch up. The human embodiment of Godwin's Law, Carson loves bringing up Nazis. He recently said that if the Jews in Europe had owned guns in the 30s, the Holocaust never would have happened. What an insightful historiography! Trump wanted in on the World War II reminiscing, so he retweeted a meme that represents the Bush family as Nazis. He then deleted it, because tweeting and deleting is kind of his thing.

Far right criticism in the upper right corner of the meme collage.

The ever-articulate, mature, and composed Trump is campaigning for president like a cyberbully, taking down an opponent with some poorly constructed memes that evoke racial stereotypes, from Nazi to Mariachi. 

He claims not to have noticed the swastika before he retweeted, because the most famous symbol of evil and totalitarianism doesn't really grab the eye.
Sources: NBC News