The media don’t claim that Trump is the frontrunner. They claim that Bush is the frontrunner, generally followed by Rubio and then Walker.
They claim, accurately, that he is leading in the polls.
Their polls that they create. So yes, they are claiming he is in the lead. And they are giving him nonstop coverage and then polls that move because of the nonstop coverage. It’s called stacking the deck. All of the sudden supposed conservatives think the media is their friend.