Over the past turbulent decade, through myriad self-inflicted troubles, Hunter Biden has relied on the kindness of friends and family — wives and girlfriends, business partners, his father and, most recently, a Los Angeles lawyer who provided the president’s son a $7 million lifeline.

But now that lawyer, Kevin Morris, who has played many parts in Mr. Biden’s life — legal adviser, confidant, strategist, art patron and friend — has told associates he is running out of liquid assets to make any more loans, deepening a chronic cash crunch that has already left Mr. Biden’s lawyers working for little or no compensation.

With Mr. Biden’s trial on gun charges set to begin on Monday in Delaware, Mr. Morris has said he might need to sell some real estate holdings or other assets if others do not step up to fill the gap, according to people familiar with the situation. He hopes to pressure the president’s advisers into helping find new donors, people close to the situation said.

Financial troubles are nothing new for President Biden’s son, and his current woes are unlikely to prevent him from mounting a sturdy defense. But it adds a layer of stress and uncertainty, and could limit his ability to hire expert witnesses or other specialists in the gun case or in his trial on tax charges in California in September, they said.

Last year, Mr. Biden was charged with lying about his drug use when he bought a .38 handgun in Delaware in 2018 and with illegally possessing the weapon. He was later charged separately with a series of tax offenses related to his failure to file returns for a number of years.

Mr. Morris has lent Mr. Biden money to cover an array of expenses he incurred in recent years, including his multimillion-dollar back taxes bill and legal expenses stemming from the government’s long-running investigation. Mr. Morris has also helped Mr. Biden on other expenses, including rent on expensive houses in Malibu and payments for a luxury car.

Some of Hunter Biden’s debts to Mr. Morris were documented by four promissory notes, totaling $5.3 million, that were reviewed by The New York Times. A fifth promissory note, detailed in a letter from Mr. Morris’s lawyers, brings the total to $6.5 million.

Mr. Biden agreed to pay 5 percent interest, with no payments due before October 2025.

But Mr. Morris has expressed growing concerns about how much longer he can soldier on, in hopes of enlisting the assistance of President Biden’s personal lawyer Bob Bauer in raising money to help pay off Hunter Biden’s debts. Mr. Bauer, the former White House counsel, handles many of the president’s most sensitive legal and political affairs.

“It is clear that there are people in the White House who would prefer Hunter would just go away, and any day he’s not in the news is a good day for the White House,” said David Jolly, a former Republican congressman who has worked with Mr. Morris to raise outside funding, with little success or cooperation from the president’s team.

“As a friend of Hunter’s, it’s hard to understand because you’d think the father’s team would do anything to protect the son,” said Mr. Jolly, who left his party in opposition to former President Donald J. Trump. “But I also understand that somebody has to make the call about how to protect the president.”

A spokeswoman for Mr. Bauer declined to comment. Mr. Morris’s money concerns were reported earlier by Politico.

Although Mr. Morris says he has never had more than a few fleeting interactions with President Biden, his involvement has stoked investigations by House Republicans. They have asked whether Mr. Morris is using the relationship with Hunter Biden to further his own interests or to provide backdoor financial help to the president’s re-election campaign.

“I’m not very popular at the White House,” Mr. Morris said in congressional testimony in January.

He said he was “confident that Hunter will repay” his loans and had no expectations of “receiving anything” from the White House.

So far, Mr. Biden’s lawyers have been willing to take on the high-profile case even though there is no guarantee how much they will be paid, if anything.

Mr. Biden’s first lawyer, Christopher J. Clark, who withdrew from both cases last summer after representing the president’s son for much of the federal investigation, took the assignment with little expectation of being fully compensated, after Mr. Bauer reached out to him.

But he has been paid virtually nothing on a legal bill estimated to be at least several million dollars, according to three people with knowledge of the situation, speaking on the condition of anonymity to discuss details intended to be private.

Mr. Biden’s current attorney in both cases, the veteran Washington lawyer Abbe Lowell, has worked while being paid only a small percentage of what he is owed on millions in legal services, which also included shepherding Mr. Biden through Republican congressional investigations, they said.

Hunter Biden’s total legal bills are expected to eventually exceed $10 million.

While Mr. Biden was once able to earn seven figures as a lawyer, investor and lobbyist, his much-publicized pivot to the fine art world has not been as lucrative. In 2020, Mr. Biden reported earning $47,734 from sales of his paintings, according to his tax returns.

In 2021, he earned $83,250 from art sales, of which $12,649 paid for supplies and labor. But over the next two years, sales appeared to accelerate. Georges Bergès, Hunter Biden’s gallerist, testified to a congressional committee that by January 2024, he had sold more than $1.5 million of Mr. Biden’s paintings, $875,000 of which were bought by a company controlled by Mr. Morris.

About a year ago, Mr. Morris recruited Mr. Jolly to help him create a legal-defense fund to cover some of the expenses, from a range of small and large donors. That plan was outlined to President Biden last year, one of the people with knowledge of the situation said, confirming a report by MSNBC. It is not clear how the president reacted.

But that effort has yielded commitments of only a few hundred thousand dollars, Mr. Jolly said.

Mr. Biden has gotten some help from others. In recent years, he has twice flown on a private plane as a guest of Joe Kiani, a tech entrepreneur and major Democratic Party donor, according to records detailing Mr. Biden’s travels that were reviewed by The Times.

Mr. Biden faces three charges related to whether he lied on a federal government form that he was required to complete for his 2018 handgun purchase in Delaware.

In response to a question on the form about whether he was using drugs, Mr. Biden said he was not — an assertion that prosecutors concluded was false. Mr. Biden has publicly acknowledged his struggles with addiction to crack cocaine and alcohol and had been in and out of rehab around the time of the gun purchase.

The first charge, of lying to a federally licensed gun dealer, carries a maximum penalty of 10 years in jail. The second, of making a false claim on the federal firearms application used to screen applicants, has a sentence of up to five years. The third, possession of an illegally obtained gun from Oct. 12 to Oct. 23, 2018, carries a maximum of 10 years.

Mr. Biden’s legal troubles appeared to be nearing an end last summer, when David C. Weiss, the Trump-appointed U.S. attorney in Delaware, announced a plea deal that would have offered immunity from future prosecution without prison time.

But the deal unraveled when Judge Maryellen Noreika of the Federal District Court in Wilmington sharply questioned elements of the deal’s structure, telling the two sides repeatedly that she had no intention of being “a rubber stamp.”

After that, Mr. Weiss decided to forgo plea negotiations with Mr. Biden. Mr. Clark, who had represented the president’s son during the negotiations, stepped aside, and his former firm, Latham & Watkins, withdrew its technical support.

He was replaced by Mr. Lowell, an aggressive and media-savvy fixture whose high-profile clientele has included Jared Kushner, Senator Robert Menendez of New Jersey and the former Democratic presidential candidate John Edwards.

Mr. Lowell has filed a flurry of mostly unsuccessful motions that have, nonetheless, aired Mr. Biden’s accusations that his prosecution was a politically motivated hit job promoted by allies of Mr. Trump.

In December, a federal grand jury in California charged Mr. Biden with evasion of a tax assessment, failure to file and pay taxes, and filing a false or fraudulent tax return. The charges, detailed in a scathing 56-page indictment, chronicled his years of drug abuse, wild spending and flouting of federal tax laws. A month later, Mr. Biden pleaded not guilty.

Mr. Morris, whatever his financial worries, remains very close to Mr. Biden. The two men speak every day, and Mr. Morris has shown no indications so far he is stepping away. He has assembled his own kitchen cabinet of advisers to help him strategize on Mr. Biden’s behalf, and plans to accompany the president’s son at both trials to offer support and advice.

“When I first met Hunter, he was emerging from the lowest point in his life — he’s had a lot of low points,” Mr. Morris told the committee when asked why he has been so generous to a man he only met in 2019.

“My only goal was and is to help my friend and client,” he added.