Is Donald Trump nearing a tipping point after which it will be difficult for any other Republican to pass him in the presidential nomination race?

Well, “nearing” might be a bit of an exaggeration, given that there are 14 GOP primaries or caucuses remaining through March 1 alone. The eventual winning nominee will have to amass 1,237 delegates. Right now Mr. Trump has 17.

But March 15 is a key date. At that point, the Republican Party will have allocated half of its total delegates. That’s the bend in the race at which the 2008 and 2012 nominees (John McCain and Mitt Romney, respectively) established clear leads.

Math is then the front-runner’s friend. Presumably one candidate will have established some political momentum to surge into the lead. Reversing that wouldn’t be impossible – but it would be very, very hard.

“Any delegate lead in either party will be difficult to close for those challenging to overtake the leader in the count at that 50 percent point,” writes Josh Putnam, a University of George political scientist and expert on nomination proceedings, at his FHQ blog.

And in regard to Trump, the facts are thus: He’s got a big poll lead in South Carolina, which holds its Republican primary this Saturday. Flip through other states on the RealClearPolitics poll aggregation site, and it’s something of a TrumpFest: The Donald has substantial leads in Nevada, Georgia, Massachusetts, Virginia, Michigan, Florida (up 21 points in the average of major surveys!), and North Carolina.

Trump trails Sen. Ted Cruz in Texas, the senator's home state. He leads in the most recent Ohio poll, but Ohio Gov. John Kasich has led other surveys, so that’s probably not a done Trump deal.

All these states hold their caucuses or primaries prior to or on March 15.

Yes, state polls can be chancy, and many of these states haven’t been extensively surveyed. But are they all wrong? Trump’s national numbers are holding up pretty well, by the way. He’s holding fairly steady with a lead of 12.7 percentage points over his second-place challenger – who is now Marco Rubio, not Senator Cruz, according to RealClearPolitics.

It’s true that the Republican National Committee intended to slow down and draw out the 2016 nomination process. To do so, it insisted that early primary and caucus states allocate delegates in proportion to vote share. Only later contests can be winner-take-all, a method that allows big gains.

But in practice, the early states aren’t entirely proportional. Many have thresholds that candidates must reach to get any delegates at all. And late states aren’t entirely winner-take-all. Nor are all rich prizes.

That means the mid-March front-runner is in an excellent position to accept the nomination in Cleveland in July. By the same token, the race might linger into April, as the pace slows and the magic winning total of 1,237 dangles just out of reach.

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“Catching up to a delegate leader and closing out a nomination become steeper climbs in such an environment,” Mr. Putnam writes.

So it’s getting late early in terms of catching Trump. It’s still entirely possible. But it might be time for the anti-Trump forces in the Republican Party to stop complaining that there are too many establishment candidates remaining in the race, and start adding up actual delegate scenarios.