This is within the current context of Donald-Trump-as-Republican-freight-train, though, not the context many (myself included) were using a month or two ago, which was, hm-I'm-skeptical. How did we get from that to where we are now? By Donald Trump consistently winning races by wide margins.
If we map the county-by-county results in the first four states to vote, you can see the evolution of Trump's dominance. A split decision in Iowa. A sweep in New Hampshire. A mixed bag in South Carolina. A romp in Nevada -- with big margins, but two important exceptions.
(In the weighted versions of these maps, the darkness of each county is scaled according to the margin of victory. The biggest margin of any victory was in Esmeralda County, Nevada, so it's the darkest.)
Let's break each of these out.
The Iowa map, in retrospect, is interesting. (The "retrospect" that comes from looking back in time three weeks.) The evangelical northwest corner went for Ted Cruz. The cities -- around Des Moines, Iowa City and Davenport -- went for Marco Rubio, presaging the arguments that he'd fare better with the more moderate part of the Republican electorate. Trump did well on the eastern edge of the state, and otherwise fought to a draw in the more rural areas. Iowa was an interesting three-way fight.
There hasn't been one since.
New Hampshire was simply a blowout. Trump won easily, across the board, as he was expected to. It didn't derail expectations much, simply because it was so expected.
And he led coming into South Carolina, but it was worth wondering if Cruz's strong turnout operation from Iowa might shift the balance of the state.
It didn't. Rubio again won cities -- around Charleston and Columbia -- but Trump won everything else. He did particularly well in Horry County, in the eastern corner of the state, won by John McCain in 2000 and 2008 and Newt Gingrich in 2012.
Then, Nevada. Trump dominated. Cruz, though, won two counties adjacent to the heavily-Mormon state of Utah: Elko and Lincoln. For Cruz to stay in the race, he needs to reconsolidate support from evangelicals and conservatives, so this, at least, is a good sign for him.
Maybe. Trump's strong performances have moved him from "lol what" to "jeez" very, very quickly. And while he's also had three straight wins in relatively friendly states, it's still not totally clear where the unfriendly states might be.