More concerning to some donors and campaign aides has been private plane use by Ms. Guilfoyle and her team, which has caught the eye of several staff members. In January, as requests started coming in for private flights, the campaign had to work out a plan for approving such trips, which must be listed as in-kind contributions or reimbursed by the campaign in order to comply with campaign finance laws.Ms. Guilfoyle’s private flights did not violate those laws, although in one case, two of her aides, without seeking prior approval, took a private flight to a fund-raising event in March. The campaign then had to reimburse for the trip at a cost of tens of thousands of dollars, according to two people familiar with the trip.Tim Murtaugh, a campaign spokesman, said that flights categorized as in-kind contributions to the campaign are funded by the donors directly. Aides said such planes had allowed for maximum attendance by top officials at multiple events per day. “In any event,” Mr. Murtaugh said, “the cost of flights and the efficiencies they provide are investments in fund-raising events that raise millions of dollars for the president’s re-election.”Through the campaign, Ms. Guilfoyle declined to be interviewed. The Trump campaign provided statements praising Ms. Guilfoyle and the campaign’s fund-raising effort from the Republican National Committee’s chairwoman, Ronna McDaniel; Jeff Miller, a veteran Republican fund-raiser; Representative Kevin McCarthy of California, the House Republican leader; and two members of the finance team.Ms. McDaniel called Ms. Guilfoyle one of Mr. Trump’s “strongest and hardest-working advocates.”The complaints about Ms. Guilfoyle’s fund-raising numbers reflect some of the harsh realities of Mr. Trump’s re-election prospects, particularly in the era of the coronavirus. A businessman who trusts almost no one, Mr. Trump has often turned to a small circle of family and friends for critical aspects of his re-election, regardless of their previous experience. That is what happened with Ms. Guilfoyle, people familiar with the situation said.And his campaign’s fund-raising, once seen as an overwhelming advantage, has lagged in the last two months behind that of his Democratic opponent, Joseph R. Biden Jr.The mid-tier donors that Ms. Guilfoyle has been tasked with developing are seen by campaign insiders as a key to closing the fund-raising gap. These donors give their own money, but also are dispatched to collect — or “bundle” — potentially significant sums from their associates.