It's apparently all part of a Democratic strategy aiming to help those seen as extremist Republican candidates to secure their Republican party's nomination. (Which Mastriano did win.)

The hope for Democrats is that those extreme Republican candidates would be much easier for Democrats to beat in the November general election. But the strategy has raised some concerns about effectiveness and whether it could have unintended consequences.

https://observer.com/2016/10/wikileaks-reveals-dnc-elevated-trump-to-help-clinton/

The memo named Trump, Sen. Ted Cruz, and Ben Carson as wanted candidates. “We need to be elevating the Pied Piper candidates so that they are leaders of the pack and tell the press to them seriously,” the memo noted.