Yes, Michael Moore can influence elections, but he can't influence this year's election in particular. Michael Moore's documentaries are always powerful and give insight on important issues. They give the public information about subjects that are important. Saying all that, this TrumpLand documentary will not make Trump lose any support because nothing else has.
Yes, Michael Moore has the power to influence elections because he always makes the headlines when he releases a new movie. If he can dig up enough old videos of Trump saying or doing bad things, the people will listen. All it takes is a video of Trump to sway a lot of voters.
Micheal Moore has a core group of followers and fans, most of whom already have made up thier mind before they watch his documentaries. He no longer has the kind of sway and influence that he used to have. He might be able to get his followers to change thier mind about particular things, but that is all.
No, Michael Moore does not have the power to influence elections, because the only people who like Moore's movies are the people who vote for liberals already. Michael Moore thinks he is a big deal, and he loves attention. But people do not take his movies seriously. Anyone that would spend the time and money to see a political movie already has an opinion.