For most of 2014 and the first nine-ish months of 2015, I thought Marco Rubio was the most likely Republican presidential nominee in 2016.

The case for the Florida senator was simple: He was young (44), Cuban American and charismatic as hell. He could straddle the chasm between tea party Republicans (he was elected in a tea party wave in 2010) and establishment types, who saw him as the next big thing in their party. He had surrounded himself with a talented and deep political team not only at the national level but also in some early states -- particularly South Carolina.

For a party desperate to change its image as the home of old, white men, Rubio seemed a godsend. He was everything that the party wanted/needed in the wake of the demographic slap in the face that the 2012 election had delivered.

Then Donald Trump happened. Trump's influence on the race has been analyzed to death, as has his ability to disrupt the chances of more establishment figures such as Rubio, Jeb Bush, Scott Walker and Chris Christie. But one thing that has been undersold is the extent to which Trump has exploded the long-held "lanes theory" of the Republican race.

Here's how the lanes theory works: The GOP electorate is split into two or, sometimes, three lanes. Candidates for the GOP nomination tend to fall into one of those lanes. The way to the nomination is to win your lane and then prove that you are more able than the other guy (or guys) (or gals) to reach into the lane they won as well.

In the 1990s and up through 2012, those lanes were the establishment lane and the social conservative lane. And, each time, the establishment candidate won that final matchup, largely because the winner of the social conservative lane couldn't get voters beyond that lane. John McCain over Mike Huckabee. Mitt Romney over Rick Santorum.

In 2016, the expectation was that the lanes theory would hold again -- albeit it with different lanes. The establishment lane was very much there, but the social conservative lane was either gone entirely or reduced to a size where it wasn't able to crown its own winner. The other big lane was the tea party lane. (There was some talk of a separate libertarian lane, but that disappeared as quickly as Rand Paul's chances of being president.)

The thinking was that the likes of Rubio, Bush, Christie, Walker and John Kasich would battle it out for the establishment lane while everyone else -- including Trump and Ted Cruz -- would fight for the tea party lane crown. Then, when the two squared off, the establishment candidate would win.

Not only did that not happen, but the entire lane structure failed at the hands of Trump's angry populism. Trump pushed his way into all of the lanes -- beating Cruz among evangelicals in South Carolina, beating Rubio among moderates in Florida. Trump lived outside the lanes theory and, in so doing, crushed it.

The simple fact is that the tectonic plates of the Republican Party have moved in a fundamental way in this race, a movement that no one -- maybe not even Donald Trump -- could have predicted when he got into the race last June.

That's not to excuse Rubio (or me).  Rubio, whom I had observed closely since he began running for the Senate in 2009 as a long-shot challenger to then-popular Gov. Charlie Crist, always had seemed ready for the big moments. He quickly became a national celebrity in that race and seemed entirely at ease when delivering much-watched speeches at CPAC in 2010 or at the Republican National Convention in 2012.

Sure, when he had the "water incident" while delivering the Republican response to President Obama's 2013 State of the Union, the excitement for Rubio within the GOP slowed somewhat.

But by the time Rubio got into the presidential race in 2015, he looked like a man who had met his moment. And even as Trump rose, there was Rubio plugging away -- avoiding direct attacks on Trump while performing as well as expected in debates. He was confident, knowledgeable and willing to throw a punch. (You could argue that Rubio as much as Trump should get credit for the demise of Bush; his put-down of Jeb during a debate in late 2015 was totally devastating.)

He finished a strong third in Iowa behind only Cruz and Trump. Polling suggested Rubio would finish second in the New Hampshire primary. Then, just days before the New Hampshire vote, Rubio froze during a debate -- repeating himself several times ("let's dispel this myth once and for all...") and looking for all the world like a robot that had blown a gasket.

He finished fifth in New Hampshire. That was the first big moment that Rubio blinked when the bright lights came on.

Moment two came about a month later when Rubio suddenly pivoted from his sunny, "new American century" message to a deeply personal attack on Trump's looks, his urinary habits and everything and anything else Rubio could think of.

The vicious personal attacks that were -- and are -- Trump's bread and butter badly backfired on Rubio. He looked petty, immature, not presidential in the least. Voters didn't like it, either; Rubio kept finishing third (or worse) as the March voting continued.

He eventually backtracked from that gutter move, telling NBC's Chuck Todd that it was a mistake and a personal embarrassment for him. Way too late. By then, Rubio's fate was sealed -- a judgment conferred on him, painfully, by his home-state voters on Tuesday night.

Rubio failed in this race for two big reasons.

The first is that he -- and everyone in the field not named "Trump" -- was operating under an old model of how you run for and win a Republican presidential nomination. Waiting (and waiting) to be the eventual establishment pick presumes that the establishment has some power to choose the nominee. There's lots and lots of evidence that, at least in this election, it does not.

The second is that Rubio just wasn't ready for the extended pressure and attention of a presidential race. At times he looked like the most charismatic, most able candidate in the field. At others, not so much. A presidential race is a long slog -- two-plus years -- but is fundamentally defined by a series of moments that happen during that time. Rubio's moments wound up being bad ones, and that made it tough for him to convince voters that he was the right man for the job right now.

Rubio's collapse, as expertly documented by my colleagues Bob Costa and Phil Rucker, is rightly analyzed as the death rattle of the establishment in this election. Rubio and I made the same mistake in this race: putting too much faith -- at least for a time -- in that establishment's ability to dictate its will on a Republican electorate that refused to play by any traditional rules and a candidate in Trump who was a tradition-breaker par excellence.