WASHINGTON — President Trump invoked the Fifth Amendment right against self-incrimination Wednesday in response to questions from the New York state attorney general’s office regarding his company’s business practices.

In explaining his silence in this matter, Mr. Trump said “I have absolutely no choice because the current Administration and many prosecutors in this Country have lost all moral and ethical bounds of decency.” 

Mr. Trump acknowledged that he once was of the opinion that “If you’re innocent, why are you taking the Fifth Amendment?” In the current circumstances, he now knows “the answer to that question.”

The one time President explained that“When your family, your company, and all the people in your orbit have become the targets of an unfounded, politically motivated Witch Hunt supported by lawyers, prosecutors, and the Fake News Media, you have no choice.”   

Mr. Trump’s refusal to testify comes amid a flurry of legal activity surrounding him, taking place just days after FBI agents searched his Mar-a-Lago estate in Florida as part of an unrelated federal probe into whether he took classified records when he left the White House.

The New York civil investigation, led by Attorney General Letitia James, involves allegations that Mr. Trump’s company, the Trump Organization, misstated the value of prized assets like golf courses and skyscrapers, misleading lenders and tax authorities.

While he was silent today, Mr. Trump was voluble last night, posting on his Truth Social platform “In New York City tonight. Seeing racist N.Y.S. Attorney General tomorrow, for a continuation of the greatest Witch Hunt in U.S. history!” 

“My great company, and myself, are being attacked from all sides,” Trump added. “Banana Republic!”

Messages seeking comment were left with Ms. James’ office and with Mr. Trump’s lawyer.

Mr. Trump’s testimony is happening at a critical point in Ms. James’ investigation, midway through a pivotal week in his post-presidency.

In May, Ms. James’ office said that it was nearing the end of its probe and that investigators had amassed substantial evidence that could support legal action, such as a lawsuit, against Mr. Trump, his company or both.

The Republican billionaire’s deposition — a legal term for sworn testimony that’s not given in court — is one of the few remaining missing pieces, the attorney general’s office said.

Two of Mr. Trump’s adult children, Donald Jr. and Ivanka, testified in the investigation in recent days, two people familiar with the matter said. The people were not authorized to speak publicly and did so on condition of anonymity.

The Trumps’ testimony had initially been planned for last month but was delayed after the July 14 death of the former president’s ex-wife, Ivana Trump, the mother of Ivanka, Donald Jr. and another son, Eric Trump, who sat for a deposition in James’ investigation in 2020.

On Friday, the Trump Organization and its longtime finance chief, Allen Weisselberg, will be in court seeking dismissal of tax fraud charges brought against them last year in the Manhattan district attorney’s parallel criminal probe.

Ms. James, a Democrat, has said in court filings that her office has uncovered “significant” evidence that Trump’s company “used fraudulent or misleading asset valuations to obtain a host of economic benefits, including loans, insurance coverage, and tax deductions.”

Ms. James alleges the Trump Organization exaggerated the value of its holdings to impress lenders or misstated what land was worth to slash its tax burden, pointing to annual financial statements given to banks to secure favorable loan terms and to financial magazines to justify Mr. Trump’s place among the world’s billionaires.

The company even exaggerated the size of Mr. Trump’s Manhattan penthouse, saying it was nearly three times its actual size — a difference in value of about $200 million, James’ office said.

Mr. Trump has denied the allegations, explaining that seeking the best valuations is a common practice in the real estate industry. He says Ms. James’ investigation is part of a politically motivated “witch hunt” and that her office is “doing everything within their corrupt discretion to interfere with my business relationships, and with the political process.”

“THERE IS NO CASE!” Mr. Trump said in a February statement, after a Manhattan judge, Arthur Engoron, ruled that James’ office had “the clear right” to question Mr. Trump and other principals in his company.

While Ms. James has explored suing Mr. Trump or his company, the Manhattan district attorney’s office has long pursued a parallel criminal investigation.

That probe had appeared to be progressing toward a possible criminal indictment, but slowed after a new district attorney, Alvin Bragg, took office in January.

A grand jury that had been hearing evidence disbanded. The top prosecutor who had been handling the probe resigned after Mr. Bragg raised questions internally about the viability of the case.

Mr. Bragg has said his investigation is continuing, which means that Mr. Trump could invoke his Fifth Amendment right against self-incrimination and decline to answer questions from Ms. James’ investigators.

According to the subpoena issued by Ms. James’ office, Mr. Trump was to appear in person at the attorney general’s office, located in a Manhattan office tower that has doubled as the fictional conglomerate Waystar Royco’s headquarters on HBO’s “Succession.”

As vociferous as Mr. Trump has been in defending himself in written statements and on the rally stage, legal experts say the same strategy could backfire in a deposition setting because anything he says could potentially be used against him or his company in the criminal investigation. No former president has ever been charged with a crime.

In fighting to block the subpoenas, lawyers for the Trumps argued New York authorities were using the civil investigation to get information for the criminal probe and that the depositions were a ploy to avoid calling them before a criminal grand jury, where state law requires they be given immunity.

Last summer, spurred by evidence uncovered by Ms. James’ office, Manhattan prosecutors filed charges against Mr. Weisselberg and the Trump Organization. Prosecutors said Mr. Weisselberg collected more than $1.7 million in off-the-books compensation.

Mr. Weisselberg and the company have pleaded not guilty.

Mr. Weisselberg and Eric Trump each invoked the Fifth Amendment more than 500 times when questioned by James’ lawyers during separate depositions in 2020, according to court papers.

The former president could choose to do the same, but it’s likely “he’ll claim lack of knowledge on many questions,” a New York University law professor, Stephen Gillers, said.

That could be a successful strategy, since Trump is known as more of a “big-picture guy,” Mr. Gillers said. “So he’ll answer the big-picture questions and those answers will be general enough to keep him out of trouble, or so his lawyers will hope.”

“On the other hand, his impetuosity makes him a lawyer’s nightmare and his overconfidence may lead him astray. Whoever questions him will encourage that,” the professor added.

Once her investigation wraps up, Ms. James could decide to bring a lawsuit and seek financial penalties against Trump or his company, or even a ban on them being involved in certain types of businesses.