Donald Trump, the poll leader for the last five months in the Republican presidential race, is about to find out whether he has permanently changed the rules of politics, or if some of those old standards still linger.

His long-promised “next phase” defined by new spending, such as a wave of television commercials, has so far failed to materialize, week after week. His advisers have not revealed the existence of any pollsters on their staff or any advertising team. He has no real research operation to examine his own vulnerabilities or those of his opponents, and, based on Federal Election Commission filings, little in the way of a voter contact operation to identify and turn out his supporters.

Regardless of how he fares in next year’s state caucuses and primaries, Trump has established himself as a political force, pushing Republicans toward a bellicose brand of populism that will linger even if he is not their standard-bearer. But he has conspicuously opted against spending in conventional ways that could fortify his lead or harm weak rivals, discarding the playbook that winning candidates have used for many decades.

“On any given day, Trump can dominate the news coverage of the entire race,” said Craig Robinson, a former Republican Party of Iowa executive director who now publishes the Iowa Republican website. “I can see how such power might make a campaign think that they don’t need to spend money on costly TV ads and direct mail.”

This strategy has so far not stopped Trump, whose campaign message is that he is a winner and who has shown a talent for attacking his rivals in new and unusual ways, from drawing 30 to 40 percent in national polls. He will most likely enter the election year atop the Republican race.

But it may have left him less strong than he could be in Iowa, where Sen. Ted Cruz of Texas has taken the lead, according to a Des Moines Register-Bloomberg Politics survey, and in crucial early states that vote immediately afterward, like New Hampshire and South Carolina. And it could make it harder for him to survive an Iowa loss.

Robinson said Trump had hurt himself in Iowa by not augmenting his news presence with a parallel effort to push his message through ads, mailers and phone banks.

“Such an effort would have also inoculated him from attack,” he said.

If Trump’s team had researched Cruz’s weaknesses, for example, then incorporated them in Trump’s heavily covered speeches and ceaseless television appearances, as well as in paid advertising, he may have been able to pre-empt or at least slow the senator’s rise there. Trump does not appear to have used a pollster to target his message or identify pockets of support, except for one survey early on.

“While leading in the polls for months and not spending any real money on advertising is novel, the Trump team needs to turn on the spending for a real advertising and turnout operation or prepare to lose Iowa and New Hampshire,” said Scott Reed, the top political strategist for the U.S. Chamber of Commerce.

Trump’s aides routinely point to the fact that he has led the polls while the person whose allies have spent the most, former Gov. Jeb Bush of Florida, is registering in the single digits.

Trump’s campaign manager, Corey Lewandowski, declined to discuss advertising strategy, but he said that the candidate had “unlimited resources and will use those to ensure his message on how to make America great again gets to as many voters as possible.”

In the past, Trump has questioned the wisdom and judgment of candidates who spent lavishly from their own pockets. He mused to Fortune magazine about the business acumen of Steve Forbes for spending so much of his own money on his own presidential efforts, and told friends in New York City he could not fathom why Michael R. Bloomberg, the three-term former mayor, had funded his own campaigns.

In 2000, when Trump was toying with a possible third-party presidential candidacy, he had a contract with the motivational speaker Tony Robbins to make $1 million for giving speeches at some of Robbins’ seminars. Fortune reported that Trump had engineered his political events so that he would give speeches in the same cities.

“It’s very possible that I could be the first presidential candidate to run and make money on it,” Trump told the magazine.

In the most recent period for which there are records, the third quarter of the year, Trump raised just under $4 million from donors. He contributed only $100,779 of his own money in that quarter, and has lent roughly $2 million since the start of the campaign.

But some of the money Trump’s campaign spends is on reimbursing him: His largest expense in the last filing period, $723,000, was on a company he owns, Tag Air, which controls the fleet of aircraft he uses to fly to all his events.

Lewandowski, the campaign manager, has said that the campaign had hired a Florida-based advertising firm. He added, almost proudly, that it was not a politically oriented company, in keeping with the outsider image Trump presents. He also said Trump was prepared to spend $100 million on a conventional television effort if needed. Then the campaign began considering other ad makers, including Rick Reed, who helped make the famous Swift Boat Veterans for Truth spots against Democratic nominee John Kerry in the 2004 presidential campaign.

But still no Trump television ads have emerged. Beyond spending just over $200,000 on a radio advertising buy last month, Trump has not made any television reservations. For a candidate fond of a deal, Trump’s resistance to put down cash on commercials ahead of time could wind up costing him more than necessary.

By waiting, he has consigned himself to pay a higher rate if and when he does buy television time. Political advertising on broadcast and cable is substantially more expensive when it is bought at the last minute, even though candidates are charged lower rates than super PACs.

What is more, the airwaves are considerably cluttered by now, with little available television time remaining. Under equal-time provisions, stations would have to find ways to accommodate him.

“Trump has already made history by pulling out to a large lead solely on the basis of free media coverage of his campaign,” said political consultant Roger Stone, who left the campaign in August but has remained a supporter of Trump.

But Stone cautioned that there was a difference between “persuasion” and “turnout,” and that the power of advertising, mailing and old-fashioned phone calls should not be discounted.

“I do think he’s going to have to use some of the traditional tools to turn his voters out,” he said.