Given the results in Iowa and New Hampshire, as well as national polls, if the Republican front-runner were a more conventional candidate we would be writing about near-inevitability. Donald Trump is in a very similar position to Mitt Romney’s at this point in 2012 – if anything, a somewhat stronger position. In 2012 Romney lagged at various points to other candidates. For Trump, this has not happened since he entered the race.

Nonetheless, what would it take for Trump to fail to get the nomination?

With the Republican field so divided after New Hampshire, the path for anyone other than Trump requires nearly all candidates to drop out. Multiple candidates want that to happen. For example, Ted Cruz thinks it is time to unite around one candidate: Ted Cruz. And so on. However, after getting 3 or 4 convention delegates each on Tuesday, Cruz, John Kasich, Jeb Bush, and Marco Rubio all have reasons to stay in. Under these conditions, Trump wins.

Many political journalists have a wrong understanding of the early-state delegate process. It is not proportional at all, but what I call pseudo-proportional. As suggested by my computational simulation of the delegate process [the code is here], in a field of four candidates, an average-across-states vote share of 30% is enough to get 50% of delegates through Super Tuesday. That’s an average: the winner could get 20% of the vote in Texas and 40% in Georgia, and so on. Donald Trump is well on track for this scenario: he won 24% of the vote in Iowa and 35% in New Hampshire. As of today, he is at 36% in national surveys.

The not-Trump scenario occurs if Republicans cull their field, fast. As far as I can tell, if Republicans want a candidate who is acceptable to most of their party to get a majority of convention delegates, their deadlines are:

Deadline 1 (February 29th): Get down to two alternatives to Donald Trump as a consequence of South Carolina and Nevada – and before voting starts on Super Tuesday, March 1st.

Get down to two alternatives to Donald Trump as a consequence of South Carolina and Nevada – and before voting starts on Super Tuesday, March 1st. Deadline 2 (March 14th): Settle on one alternative to Trump as a consequence of Super Tuesday and the March 5th-12th primaries.

For example, the first of these deadlines can be met if the South Carolina and Nevada primaries knock out three of the following four: Bush, Kasich, Rubio, and Carson. (I’m assuming that at a minimum, Cruz is in through Super Tuesday.)

If these drop-dead dates aren’t met, Trump could still be stopped, but it would be difficult. First, it would require somebody other than Trump to take the popular lead in April. In a three-way race, that is hard to imagine. Even in a two-way race, it is not at all clear that Trump will lose, since for now, he picks up enough “Establishment” support in head-to-head matchups to get a majority. Consistent with this, exit polls in New Hampshire show that some Republicans of all stripes like Trump.

To understand the details, let’s get into the weeds of the delegate process.

Look at the rightmost column of The Green Papers table showing the timetable of cumulative delegates, including links to the delegate-selection rules. The basic principles are (a) state GOP rules are seldom truly proportional, evading a mandate from the national party; and (b) all delegates (including party officials, who used to have more discretion) are required to vote for their assigned candidate on the first ballot. Basically, state parties created loopholes to tilt the balance toward the front-runner, while giving the appearance of proportionality. This may have been to give themselves more leverage. National rules say delegates who don’t vote for their candidate on the first ballot risk getting their credentials stripped. These two principles have painted the GOP into a corner.

The closest that state contests get to proportional is now through March 8th. But as I have mentioned, these races are pseudo-proportional. For example, in New Hampshire, Donald Trump won 36% of the vote but got 43% of the delegates. In South Carolina, I estimate that a 37% vote share would get him over 90% of the delegates.

On Super Tuesday on March 1, 25 percent of all delegates are assigned, mostly pseudo-proportionally. On March 5-12, races are pseudo-proportional for an additional 9 percent of delegates.

After March 12th, things get even better for the front-runner, whoever it is. On March 15th, three states are either winner-take-all (Florida and Ohio) or winner-take-nearly-all (Missouri) for another 9 percent of delegates. Anti-Trump forces would be well advised to get down to one alternative before then. However, that would require Ohioan John Kasich and/or Floridians Marco Rubio and Jeb Bush to get themselves down to one candidate within the coming four weeks. In a tragedy of the commons, driven in part by super-PAC money which is not attached to the Republican Party, such self-elimination looks unlikely.

If Trump gets over 50% of delegates through Super Tuesday, Republican operatives are likely to fall into line and support him. They are already doing that, if Bob Dole’s words are any indication. Ballpark, I would guess that if Trump has a majority of delegates by March 1st and he still has two opponents afterward, his probability of securing the nomination will be about 80%. However, this is now my intuition talking.

If nobody has a clear majority by mid-March, how long will the process likely drag on? Last week Ben Ginsberg (the Bush/Cheney campaign lawyer) said in a presentation at the Stanford Law School that in past years, a presumptive nominee emerges around the time that 68% to 71% of all delegates are assigned. In 2016, that happens on April 19th with the New York primary. Since votes are votes (i.e. they count whether for the Establishment or for a strange entity like Donald Trump), we should know by then.