The media right now is pushing the narrative that Trump is inevitable, the contest is over, he has won. They have obvious reasons for doing this - they want to convince Republican voters that the contest is over so they can enjoy the ratings that come from the public flogging of a lunatic for several months.
The main problem with this narrative is that the voters are not buying it. There have been two polls that have been taken since the South Carolina primary, which was supposed to be Trump's victory lap, and one shows Trump at 31%, and the other at 36% - exactly where he has been throughout this primary season, if not lower.
The media is slow to get this message even though the evidence is staring them in the face, so let me state the point simply: Trump does not get bounces from performing well in primaries. The media treats Trump's win as inevitable because any other candidate in Republican history who won 3 of the first four contests pretty handily would have received a bounce from his victories. Furthermore, as other candidates would have dropped out of the race, the front runner would have picked up some portion of them. Trump has not.
In fact, Trump's overall standing in the national polls has gone down since Iowa. The media is not paying attention to the numbers, so let's draw them a pretty picture instead, from RCP:
See that? Absolutely bupkis. Trump peaked in Mid-December at about 36% and has actually been on a very slow downward arc since then.
Now let's draw a DIFFERENT pretty picture (actually, it's not that pretty. My artwork sucks. I'm a blogger, not a graphic designer). This one shows 2012.
See how this is different? Rick Santorum won Iowa, and he went up nationally by 12 points overnight. Romney won New Hampshire, and went up 8.5 points overnight. Gingrich won South Carolina, and he went up 13 points. Romney responded by winning Nevada in convincing fashion, and he went back up 9 points nationally.
This is a fundamentally different phenomenon than what we have seen in years past I could draw equivalent pictures for every contested election. In 2008, Huckabee got an 11 point national boost from winning Iowa. McCain got a boost from a surprisingly strong Iowa finish, and a bigger one from winning New Hampshire, and he never looked back. RCP doesn't have pretty graphs that go back further on the Republican side, but this has always been the case.
It happens for a couple different reasons. It happens because people buy into inevitability and love a winner. And it also happens because almost every contest eliminates someone, and eliminated candidates' supporters go in some portion to the front runner. Neither of those things have happened this year and the media is failing to notice it.
That is also true on the statewide level. After winning New Hampshire in convincing fashion, Trump's standing in the polls in South Carolina did not go up, and in fact he ended up with a finish in the low-30s, as expected. His win in South Carolina did not boost him in Nevada.
Trump is still ahead because the field remains ridiculously fractured behind him due to some deluded idiots (thanks, Kasich and Carson!), but he's absolutely not gaining steam towards the point where he's inevitable.