Silver doesn't recognize that this election isn't a typical election; we are at a special time in history. There is a demographic of people that understand that the world is changing, and they do not like it. This cultural shift, which I'm not smart enough to really delve into, is encouraging the dying, furious gasps of a group of people furiously trying to hold on to a country that isn't coming back.
Thus, you have Trump, Carson, and Cruz at the top of the charts. Note that someone like Walker didn't gain traction; the folks voting for Trump, Carson, and Cruz are economic populists, which explains the quick death that Walker (thankfully) died in the primary season. These folks are culture warriors. They respond to Trump putting Fiorina "in her place," a fear of Planned Parenthood, a fear of Muslims, a fear of Mexicans, a fear of black folks, LGBTQ folks, etc.
Think about how quickly we went from anti-miscegenation laws to gay marriage in this country. A little over forty years - nothing in terms of the scale of human history. If you're a sixty-year-old voter who subscribes to past cultural norms, it must seem like the world has gone mad to you.
That explains both why Trump leads (economic populism + culture warrior rhetoric) and why Silver's underlying assumptions about this primary season are incorrect, IMO.
Here's how I see it. Republican voters are sliding towards irrelevance. Like their party, they are becoming more and more extreme, and more and more of the country at large are looking at that extreme and going... fuck no. The voters got in a bunch of candidates who played to the tea party, without getting their hands too dirty with the extreme beliefs... but then those candidates didn't do the crap they told the extremists they were going to do, like repeal Obamacare, etc.
Then along comes Trump.
Instead of subtly playing to the people who feel like they have 'lost' their America to the foreigners, to the Muslims, to the gays, to feminists etc etc, without condemning any of those groups, Trump is just like yeah, I hate all that stuff too. Apart from the gays. But fuck Brown people. And women. You know?
And those voters go... HE SAID IT! HE SAID WHAT WE THINK! WE LOVE HIM!
And the other candidates must have all gone... Oh shit. He said it. No we either have to be outwardly racist too, to play to the extreme base of our voters but definitely taking a position the country disagrees with, or we have to take a position that's a lot safer in the general election and just hope that those voters eventually move away from Trump... because if they don't... we're fucked.
When they made all those gains in the house and senate last year, they must have thought they were in a really great position for 2016's presidential elections.
However, as Republicans often do, they took an easy short term gain, without releasing the mistake they were making long term.
Obama's election in 2012 proved that a Republican can no longer win by just appealing to the white adult male vote. They ran their standard strategy against a President that on paper should have been quite beatable... but what happened was all those groups they normally ignore all voted the other way, and Obama won by a land slide.
The day after the 2012 election they should have started trying to package their core ideals of small government and low taxes etc to appeal to these groups if they wanted any chance in 2016.
Instead they went the other way, sucked in by the passion of the bigots who are being louder than ever because they've realised that public opinion has finally broken against them.
They made gains in 2014 because of incredibly low turn out. Nothing more. Nothing less. And the angry passionate extremists who turned out, have now soured on politicians to the point where they're prepared to vote for anything but a politician.
If a candidate that appeals to them makes it onto the ticket next year... they're fucked basically... and Trump has forced everyone in the primaries to either stand with the extremists or against them.
Nate is banking on the fact that the majority of republican primary voters are not extreme crazies. But add those Carson numbers to Trumps, and you aren't far off 50%. And the Carson voters aren't going to move to Rubio.
Rubio absolutely has a chance... and if they want to have any chance beyond 2016 of staying relevant the Republican party has to hope he wins. But they have to ask themselves, are they willing to give up the fight over gay marriage, or the fight over abortion, or the fight over the affordable care act, and go back to their core beliefs (that absolutely can appeal to people of all walks of life)... because we're moving increasingly towards that being necessary for them.