Donald Trump’s ‘Self-Funding’ Stalls G.O.P. in Donor-Data Collection -

He often brags that he is paying for his campaign, saying, “I don’t need anybody’s money.”

But Donald J. Trump’s disregard for fund-raising by email, building lists of small-dollar donors and assembling a modern campaign digital operation could hamstring him as a general-election candidate and do lasting damage to the Republican Party, strategists say.

In 2013 and 2014, one of the most valuable assets for Republican candidates at every level was Mitt Romney’s email list, containing the names and contact information for his donors, volunteers and supporters — a trove that had been amassed, culled and refined over 18 months of the 2012 campaign.

That required painstaking work, including frequent communications with supporters in hopes of conditioning them to donate repeatedly. And it paved the way for candidates to send emails to a vast, inherited universe of potential contributors who could easily make gifts with one click.

Mr. Trump, however, has emailed no mass requests for contributions or for petition-style statements of support on various issues, as many candidates do to collect names and email addresses, aides confirmed. Rather, he has passively harvested the contact information of people who choose to visit his website and donate or buy campaign-themed merchandise.

Many of his supporters, moreover, are first-time or infrequent voters or political independents who may not already show up in the email lists that Mr. Romney and other Republican list-builders have previously gathered.

To specialists in political data operations, an enormous potential reservoir of money and information is being squandered.

Graphic | How the Rest of the Delegate Race Could Unfold An interactive delegate calculator that lets you simulate how the 2016 Republican nomination process could unfold.

“This primary is an unusually intense period of actions being taken by record amounts of people in our primary contests,” said Brian Stobie, a partner at Optimus, a Republican digital firm, who helped run Senator Marco Rubio’s data operation in this cycle. “Unfortunately, it looks like that activity is not being captured and archived by one of our major presidential campaigns, and that represents a missed opportunity for the party.”

Each day that goes by, Republican strategists say, is a lost chance.

“Time is one of the most important assets of building a small-dollar donor program,” said Chris Georgia, who led Jeb Bush’s digital efforts in this race and the National Republican Congressional Committee’soperationin 2014. “And you can’t make up for the 16 months up until now that there hasn’t been any real development of that going on.”

Mr. Georgia said the Romney list was vital to the Republican congressional committee’s small-dollar donation program. “There are obviously other sources that you can prospect through and grow your list from,” he said. “But the size of that list and the quality of those donors can only happen from a presidential election, and we don’t have that this time around.”

Mr. Trump’s aides insist that his financial wherewithal frees him from having to fund-raise, and that even so, partly by requiring supporters to request tickets to his rallies through an online form, they have collected millions of email addresses they will be able to use should he become the nominee and opt to aid other candidates.

“What happens traditionally in a campaign is they will go out to their list once or twice a week to raise money from their fund-raisers, but when a candidate gets to a general election, you get some donor fatigue because they’ve already maxed out their campaign to give,” said Corey Lewandowski, the Trump campaign manager. “Our list is exactly the opposite.”

Mr. Lewandowski added that Mr. Trump’s social media following reduced the need for a cultivated email list, and that his supporters were so motivated, they would not need much coaxing if he did decide to ask them for money.

Mr. Trump has not completely ignored fund-raising: His website has two “donate” buttons, and he has reaped $9.2 million in small-dollar donations. (By comparison, he has lent his campaign a total of $36 million, his latest campaign finance reports show.)

Interactive Feature | Sign Up for the First Draft Newsletter Subscribe for updates on the 2016 presidential race, the White House and Congress, delivered to your inbox Monday through Friday.

But the credit-card numbers used to make those gifts could be of enormous potential value to Republicans if he worked at expanding the number of supporters who donate.

Mr. Trump is using software from Targeted Victory, a leading Republican digital firm, to process credit-card transactions. If another candidate uses the same software later, voters who previously created an account to give to Mr. Trump would simply have to choose the amount they want to donate, then click one button to process the transaction.

Zac Moffat, a co-founder of Targeted Victory and former digital director for Mr. Romney, said he believed that the Trump campaign had intentionally bypassed a full-blown effort to raise money online — despite the fact that hundreds of millions of dollars would need to be spent on the general election.

“Easily he’s left tens of millions of dollars of fund-raising potential on the table,” Mr. Moffat said. “But that wasn’t the campaign they wanted to execute. These are strategic decisions. It’s not like this is a surprise to them.”

Mr. Moffat also said there was still time for Mr. Trump’s campaign to start a robust email program: “Sixty to 70 percent of the growth is going to come in the last five months,” he said.

And there are already some signs that Mr. Trump may change course. His newest lieutenants, Rick Wiley and Paul Manafort, have hinted at adopting more conventional campaign tactics. A day after Mr. Wiley was hired as political director, the Trump campaign emailed supporters offering “New York Values” T-shirts, stickers and other campaign gear for sale. And after Mr. Trump’s victory in the New York primary on Tuesday, his campaign texted supporters a message steering them to the campaign’s online merchandise store.

De-emphasizing digital campaign work up till now has put Mr. Trump out of step with key efforts of the three biggest Republican umbrella organizations — the party’s national committee, and Senate and House campaign arms — each of which made investing in digital and data operations central to its strategy after Mr. Romney’s loss to President Obama in the 2012 election.

The national committee’s email team alone is four times the size of the whole 2012 digital team and has been steadily adding to its email list and data to prepare for the 2016 general election, a list it will have ready to turn over to the eventual nominee, which could end up helping to jump-start efforts in the future by Mr. Trump should he choose to use it.