Any release of damaging information about a party involved in an election can change the result. This has not been a problem before when Wikileaks almost definitely influenced the result of Kenyan election in 2007. Assange even got an Amnesty International award for leaking information then.

There's loads.

Trump standing up on a podium and asking Russia for help and then retweeting the leaks.

It had such an impact one lunatic entered a pizza parlour with a gun and another posted pipe bombs to the clintons , Obama , Soros etc.