Fineman's reasons are unconvincing -- no, Trump is not going to win Florida, given his off-the-charts unfavorability among Hispanics there, including Cuban-Americans -- but one of the reasons is worth pondering, whether or not it's going to be a game-changer:
Journalistic Weakness. It comes in two flavors. One is false equivalence. Reporters have yet to fully examine Trump’s record, especially the details of his business dealings and personal life, but soon enough his story will be yoked with and compared to Clinton’s, which will make it easier for Trump to slide by in the resulting din."Reporters have yet to fully examine Trump’s record, especially the details of his business dealings and personal life, but soon enough his story will be yoked with and compared to Clinton’s" -- that's really going to happen, folks. Yes, the Clinton campaign and its surrogates will bring up Trump University and Trump's bankruptcies and Trump's mob ties and history of racial discrimination -- but these stories will reported with the asterisk "On the other hand, the Clinton Foundation blah blah blah blah blah," or "In the 1990s, Mrs. Clinton's cattle-future trading was investigated...." Both Sides Do It, so the press will feel the need to yoke every Trump scandal to a Clinton scandal. This tendency is likely to be extended even to such matters as Trump's racism: Yes, Trump calls Mexicans "rapists" and wants to ban Muslims, but Hillary Clinton said "off the reservation" that one time.
The second flavor is the media’s hunger for an audience. The closer Trump gets to the White House, the more frightening he becomes, the more desperate his enemies become -- the more eyeballs are focused on smartphones and TV sets.
That means more billions in “free” media for Trump.
And on Fineman's second point, it's quite possible that we'll still get comment-free unedited coverage of Trump rallies -- more so than of Clinton's -- simply because he's better television. I'm not sure it will matter -- there'll be saturation coverage of both campaigns -- but I think, on balance, when the wonks run their analyses of the 2016 general election campaign, it'll be Clinton, not Trump, whose coverage is more negative, by a considerable degree, if only because so much coverage of Trump involves stepping back and just letting him hold forth. This, of course, would be a continuation of a pattern we've already seen in the primaries:

I still think Clinton will win -- but the press will keep the race close.