There's several not-so-subtle layers of irony to this tweet, which makes it all the more hilarious.
Firstly, the reason he is bringing up Clinton "collusion" with the DNC is to defend against accusations against him and his campaign possibly colluding with Russia in the 2016 election. Ignoring that colluding with a hostile foreign government to get elected is magnitudes worse than colluding with a political party inside the US to get elected, he almost seems to be excusing working with Russia. "If Clinton wasn't attacked for this, why should I be?!?" Hint: she was, it's probably a big reason why she lost.
Secondly, nearly all of the "evidence" (about half a dozen emails possibly taken out of context) of Clinton-DNC collusion has been provided by Wikileaks and Russia due to a hack made specifically to hurt Clinton's chances and help Trump's. Not only that, but this "evidence" is currently being investigated by the FBI as to whether it was released because of collusion between Russia and the Donald Trump campaign.
So not only is the tweet projection to the max (as is Trump's style), it is made on the basis of emails released by Russia, possibly due to collusion between the Trump campaign and Russia! You can't make this shit up, people.