“Whatever a man soweth, that shall he also reap.” The proverb comes from the Bible, specifically Galatians 6:7 — shortly after President Trump’s favorite book, “One Corinthians.”

If anyone would seem to be immune from this divine justice, it’s Trump. Yet, even he might begin to experience its gravitational pull.

Long notorious for his mistreatment of lieutenants and business partners, Trump may finally be reaping what he has sown, as those he has shirked or humiliated are turning on him with increasing rapidity. This creates critical opportunities for those investigating Trump in the impeachment inquiry.

Prosecutors and investigators always look out for mistreated ex-associates who can help bring down a target. Testifying is a heavy burden — especially when the testimony is against someone like Trump, who has power and a penchant for abusing it. Anything that can provide a witness with additional courage to come forward is always welcome, and sometimes that courage comes from a witness’s desire to set things right even when they themselves were wronged.

The New York attorney general’s civil prosecution of Trump University in 2013, which I helped lead, was a prime example. The Trump Organization’s lawyers were not cooperating with our investigation. They were stonewalling us, only giving us a small percentage of the documents we had subpoenaed from them.

So we expanded the scope of our search, subpoenaing third parties we believed held relevant records. These were mostly vendors to whom Trump University and the Trump Organization outsourced various business functions, from employee background checks to conducting and transcribing seminars to preparing the “curriculum.”

The Trump Organization was and is the primary holding company for the Trump family’s businesses, each of which is a limited liability company, or LLC. Trump University was an LLC, mostly owned by two other LLCs, which in turn were owned by Trump — a Russian nesting doll of corporate entities, you could say. The point was to make the LLCs “bankruptcy remote,” meaning any of them could default or declare bankruptcy without affecting the Trump Organization. If one LLC was shut down, it could shirk its debts and obligations, rather than having the Trump Organization step in to handle final payments.

Consequently, when Trump pulled the plug on his illegal, fraudulent “university” in 2010, his team engaged in a standard Trump Organization practice: It refused to honor its outstanding obligations. Instead, the team sent creditors a letter with a release agreement, offering to pay 30 percent of the balance, on a take-it-or-leave-it basis. They did this with all remaining invoices, even for a hotel where one of the seminars had been held. And sometimes they refused to pay anything at all.

Through discovery in our lawsuit against Trump, we obtained emails from vendors whom the Trump team had refused to pay — with some outstanding invoices above $10,000 each. One vendor, who we believed held critical documents, was initially reluctant to speak to us, but once I asked about their unpaid invoice, it was like I had flipped a switch. The evidence they provided was crucial in corroborating our witnesses and allowing us to make a much stronger case against Trump University, resulting in a $25 million settlement.

Trump’s practice of stiffing his partners when parting ways is part of a broader pattern of behavior. He seems to have a deep-seated urge to humiliate a counterparty, even when the other person or entity is an erstwhile friend, and even when the shrewd move would be to placate. To Trump, revenge is a dish best served immediately, in public and as scalding as possible.

But humiliation breeds resentment. Rather than retaining departed partners as allies, or at least neutral parties, he turns them into adverse parties who may reappear to share what they know — especially now as he fights impeachment.

That’s what has been happening in the House Intelligence Committee’s impeachment proceedings.

Former U.S. ambassador to Ukraine Marie Yovanovitch joined the Foreign Service in 1986 and has served as an ambassador in Republican and Democratic administrations. But in May, Trump abruptly recalled her, apparently after a smear campaign by Trump’s personal lawyer, Rudolph W. Giuliani, and Giuliani’s now-indicted associates, Lev Parnas and Igor Fruman. Trump bragged about the firing to Ukrainian President Volodymyr Zelensky. Then while Yovanovitch was testifying in the impeachment hearing on Friday, Trump blasted her on Twitter.

Yovanovitch’s response was seen Friday in her unwavering testimony, which even drew praise from Fox News anchor Chris Wallace, as she methodically dissected the campaign against her and the hijacking of American foreign policy by Trump and his inner circle. While Ken Starr stated that Trump’s tweets against Yovanovitch showed “extraordinarily poor judgment,” risking a charge of witness tampering, Trump cannot help himself. He did the same thing this weekend, slamming Vice President Pence’s aide, Jennifer Williams, two days before she, too, was set to testify.

Former national security adviser John Bolton could be in a position to do the same thing. The longtime conservative aide and Fox News commentator worked in Trump’s White House until September. Senior advisers come and go (especially in this administration), but Trump took special relish in kicking Bolton on his way out the door. Bolton claims he offered to resign on Sept. 9, and Trump said: “Let’s talk about it tomorrow.” On Sept. 10, Trump tweeted that Bolton’s “services were no longer needed” and that he had asked for Bolton’s resignation — i.e., that he fired Bolton.

Bolton, through his attorney, has affirmed his willingness to testify in the impeachment hearings, even teasing that Bolton knows about “many relevant meetings and conversations that have not been discussed in the testimonies thus far.” He may want the cover of a court order upholding a subpoena before he heads to Capitol Hill, but it seems he would love to tell the world what he knows about Trump and Ukraine.

Even when Trump isn’t firing someone but simply not hiring them, he still engages in a weird ritual of domination. When Trump was publicly considering 2012 GOP nominee Mitt Romney for secretary of state before he took office, the two men met for a now-infamous five-star dinner in New York. Yet the (now-convicted) Trump adviser Roger Stone said the dinner was Trump’s way of “toying” with Romney, a form of “torture.” Rather than politely informing Romney that he was not the pick, Trump poured gourmet sea salt in the wound.

Once again, Trump made an unnecessary enemy who could cause him significant harm. Rather than remaining in retirement, Romney reentered political life by nabbing a Senate seat from Utah. Trump may not be the sole reason for Romney’s return to politics, but Romney’s very presence in the Senate is a political liability for Trump. Romney castigated Trump’s withdrawal of U.S. troops from northern Syria and its subsequent takeover by Russian and Turkish forces. (This drew return fire from Trump, who called Romney a “pompous ass.”) And Romney became the first GOP senator to say he has a “completely open mind” on removing Trump from office.

Even bigger dangers lurk ahead for Trump, depending on how he treats his remaining allies. Mick Mulvaney has had the humiliating “acting” qualifier next to his “chief of staff” title for 10 months now. Testimony on Wednesday by Gordon Sondland, the U.S. ambassador to the European Union, confirmed Trump was in control of masterminding the effort to use U.S. aid to Ukraine as leverage to benefit his reelection — and Trump, perhaps mindful of the possibility that criticism could backfire, claimed he “didn’t know him very well” but he “seems like a nice guy.”

Generally, Trump’s reaction when past associates turn on him has not been stellar. Just ask Michael Cohen or Anthony Scaramucci or Omarosa Manigault Newman. Trump could still easily unleash a vindictive tweetstorm at Sondland: He noted on Wednesday night, while Sondland was flying back to his job in Brussels, that Sondland’s lawyers are Democrats.

Then there’s Giuliani. There are rumors that Trump plans to scapegoat Giuliani, one of his most dutiful supporters for years, if the impeachment hearings get too close to the Oval Office. But that may be one betrayal too many for Trump: For Giuliani, who has been acting as Trump’s personal lawyer during impeachment, to tell all he knows could be ruinous to Trump.

Or perhaps in the end, Trump will still prevail, despite alienating everyone who comes near him. With enemies like these, who needs friends?