Fort Worth, Texas(CNN) Donald Trump may be on the verge of becoming the presumptive Republican presidential nominee after running one of the most unorthodox campaigns in modern history.
He doesn't spend big on direct mail or paid advertising, often letting his rivals take over the airwaves. He largely eschewed the retail politics so popular in early-voting states and made comments that would sink any other politician.
Trump's expectation-defying campaign is about to face its biggest challenge, and potentially its biggest payout, when voters hit the polls in delegate-rich battles from Georgia to Massachusetts on Super Tuesday. They'll face the same dynamic again March 15 when crucial states including Florida, Illinois and North Carolina vote.
For the first time, Trump's low budget-campaign --- which depends largely on free media, public polling and a free-wheeling candidate who jumps from one controversial comment to another -- will have to make calculated decisions about how to spread its resources.
While Trump's unconventional playbook has drawn its share of skeptical reviews from political operatives, several Republican campaign veterans expect Trump's tactics will deliver big dividends on Super Tuesday.
"The last thing I'm in a position to do is give a guy advice who just whomped us," said Chip Saltsman, former campaign manager and senior adviser to former Arkansas Gov. Mike Huckabee's two presidential campaigns. "Whatever is working for him, don't break it."
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Even as Trump's opponents and their super PACs dwarfed Trump's spending on direct mail and paid advertising, Trump has still managed to dominate the airwaves. But some strategists said traditional campaign investments, such as television advertising, could take on added importance with several states voting at once.
And Trump should be prepared, they said, to make bigger investments to guarantee victory on Super Tuesday and beyond, when the celebrity candidate will be spread more thinly.
"If he doesn't have a big night because of a desire for cost saving, you know that will set him back," said Matt Schlapp, former political director to President George W. Bush and the current chairman of the American Conservative Union. "I don't think that they will refrain from writing the checks that are necessary...I gotta believe they're smarter than that."
Trump's South Carolina operation embodied the campaign's successful lean approach. But it also highlighted opportunities Trump may have missed to win late-breaking voters and the risks of relying on outlandish comments to dominate the airwaves.
For months, Trump's team of veteran GOP operatives in South Carolina struggled to win the resources they felt they needed from the campaign's national headquarters. Requests from South Carolina staff to boost spending on paid media or launch a direct mail operation languished, two sources with knowledge of the campaign's internal workings told CNN.
The Trump campaign spent just $1.6 million on TV advertising -- a number dwarfed by rival campaigns' spending -- and, aside from a Christmas card sent to supporters, had no direct mail operation to speak of.
Meanwhile, with the South Carolina airwaves saturated with ads knocking Trump or boosting his opponents, 23% of voters made up their minds about who to support in the final days before the primary.
For the most part, they sided with candidates not named Trump. More than half of those late breakers ended up voting for either Rubio or Cruz, with just 14% settling on Trump in the final days, according to exit polls.
Data from rival campaigns showed Trump's rocky debate performance, in which he said George W. Bush didn't do enough to prevent 9/11 and lied about the existence of weapons of mass destruction in Iraq, dented his margins with evangelical voters.
Corey Lewandowski, Trump's campaign manager, denied that Trump has ever deprived states of the resources they requested.
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"I can tell you, because I have the privilege of running this campaign, Mr. Trump has never said no to a funding request," Lewandowski said.
Jim Merrill, the campaign's state director, said he would have ideally fronted a bigger advertising response to counter the anti-Trump attack ads, but the campaign's lean operation still prevailed.
"I would have loved to have responded to $50 million of negative advertising, but in the end Mr. Trump's message got through to South Carolinians. So clearly I was wrong," Merrill said.
Trump managed to win by a comfortable 10-point margin, but it raised new questions about the billionaire candidate's willingness to shell out significant sums of money to win more hotly contested states where he lacks the caliber of political veterans -- and months long, double-digit leads -- he enjoyed in South Carolina.
The Trump campaign has relied on staff and volunteers in states further down the field to bolster its outreach in upcoming contests. For instance, volunteers in Michigan phone-banked to help persuade South Carolinians to turn out for Trump. And several staffers from the campaign's New Hampshire office went on to help the effort in South Carolina and are now moving into the March states.
But deciding where to devote those resources -- and determining which states are still in flux rather than firmly in Trump's corner -- can be tougher without a sophisticated data operation or internal polling.
Lewandowski, the campaign manager, said his goal is simple: Put his celebrity candidate on display as frequently as possible, in as many states as possible: "People want to see Trump."
Veteran Republican operatives who once questioned the Trump campaign's tactics are now beginning to respect the effectiveness of his approach.
"He's absolutely dominating the earned media battle," said GOP strategist and CNN political commentator Kevin Madden. "He has blocked out the sun for all of the other candidates."
Mike DuHaime, New Jersey Gov. Chris Christie's 2016 senior strategist, said Trump may not have won late-breaking voters even if he spent more on air.
"Late breakers tend to be late breakers because they already have a reason to not be with the front runner," DuHaime said. "Late breakers tend to go with the challenger, not the incumbent."
Given Trump's media domination, DuHaime said, he's "kind of like the incumbent."
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A new raft of spending from the Trump campaign suggests his team may be making adjustments. Trump dropped $1.55 million on ads in six southern primary states Friday -- nearly as much as it spent in South Carolina altogether.
That figure still puts Trump more than $1 million behind the Cruz campaign's Super Tuesday ad spending and $1.5 million behind a super PAC backing Rubio, according to Kantar Media/CMAG.
A portion of Trump's spending is being funneled to Texas, where he hopes to beat Cruz. But other buys are in states that rival campaigns view as safely in Trump's corner.
Meanwhile, Trump's smallest ad buy was in Arkansas, and he has so far spent nothing on TV in Oklahoma -- both states the Cruz campaign believes it can win based on its internal polls, according to a Cruz adviser.
Trump's fitful messaging strategy has also defied conventional political wisdom, which suggests candidates should home in on a core message and hit issues that will resonate locally -- something Trump's team of South Carolina operatives struggled to do.
As Trump faced attacks over his past support for gun control measures and abortion rights, those operatives were eager to pivot to Trump's tough stance on terrorism by setting up a news conference in Hanahan, South Carolina, home to a military prison the Pentagon is considering as a new host for Guantanamo detainees.
Trump would open with a statement slamming that plan and vowing to keep Guantanamo open.
Instead, Trump took the podium with his own agenda. He threatened a lawsuit against Cruz and slammed the Texas senator as "unstable," and a "basket case." Guantanamo, which didn't come up until halfway through the press conference, became a footnote.
The news conference would make all the primetime newscasts that evening, but some of Trump's aides felt it was a missed opportunity, according to one person with knowledge of the press conference.
In the final days before the primary, Trump drove the national media narrative with an unrelenting volley of attacks on Cruz, claims that George W. Bush lied about the existence of weapons of mass destruction in Iraq and even a feud with the Pope.
And it worked.