In the most recent instance, on Wednesday, the department took Trump’s side in a federal lawsuit against the Manhattan district attorney. In that case, Trump has sought to block a subpoena for his tax returns — using the precedent-shattering argument that a sitting president shouldn’t be investigated by any prosecutor, for any reason, anywhere.

The Justice Department didn’t explicitly embrace Trump’s broad arguments. But it did urge the judge in the case to take extra time to consider them, given “the weighty constitutional issues involved.”

The Justice Department has long defended presidents when they’ve been sued. Now it is also jumping in to support Trump when he sues others — backing him up as he pushes for an expansion of presidential immunity.

“The DOJ has elected to insert itself into this private lawsuit to support [Trump’s] extravagant claim” of presidential privilege, District Attorney Cyrus Vance (D) wrote in a letter to the judge Thursday.

Vance accused the Justice Department of helping Trump avoid investigation, by playing for time: “[Trump’s] only goal in this litigation, now supported by the DOJ itself, is to obtain as much delay as possible, through litigation, stays, and appeals.”

Some critics of Trump are hoping that the new impeachment inquiry launched by House Democrats — while not connected to any of these existing suits — may help speed their path through the federal judiciary. The argument would be that, if Congress needs to know something about Trump’s private conduct, now is the time.

“The clock is ticking on this presidential term,” said Brianne Gorod, chief counsel of the Constitutional Accountability Center, which is seeking records about Trump’s private business dealings with foreign governments. “Where the House is seeking information that is relevant to its determination whether to impeach the president, it needs that information as quickly as possible.”

But it’s too early to tell whether that will be the case — or if, instead, the House’s focus on a separate investigation into Trump’s dealings with Ukraine will sap the urgency from these cases.

During Trump’s term, federal lawyers have defended him against three lawsuits alleging he is violating the Constitution by continuing to do business with foreign governments through his family business. Two of those lawsuits, which focus on the Constitution’s “foreign emoluments” clause, are still pending. Another was dismissed, but the plaintiffs are asking for a rehearing.

But, under Trump, the department has also taken on an expanded role — as legal firepower to a highly litigious president, who has carried over his longtime habit of using lawsuits to stymie his enemies.

For Trump, “the idea is to beat the system,” even if he can’t beat the cases, said James D. Zirin, a former federal prosecutor and the author of a new book called “Plaintiff in Chief: A Portrait of Donald Trump in 3,500 Lawsuits.” “It’ll achieve delay. . . . The wheels of justice grind very slowly.”

Jay Sekulow, a private attorney for Trump, said his team consults with the Justice Department when necessary. The team Sekulow oversees has the job of advocating for the president’s personal interests. The Justice Department has an interest in preserving executive authority.

The two confer, he said, when Trump’s personal arguments intersect in some way with presidential power. He noted that, in two cases, a judge actually asked the Justice Department if it wanted to intervene.

“Any discussions that would take place would be because of the institutional interests the Justice Department would have regarding legal issues we had raised, to include, [constitutional] authority, separation of powers, among other things,” Sekulow said. He said the consultations usually involve William Consovoy, another private attorney for Trump, and James M. Burnham, a deputy assistant attorney general.

“The courts have asked for the views of the Justice Department, which is typical in these kinds of cases, going back to President Clinton,” Sekulow said.

The Justice Department declined to comment for this story.

In two other cases, the Justice Department has supported Trump as he seeks to block congressional investigations of his finances — by suing the committees investigating him, and suing the companies the committees subpoenaed for records.

One of those cases involves a House Oversight Committee subpoena to Trump’s accountants, Mazars USA, seeking his tax returns.

The other involves subpoenas to two of Trump’s banks, Deutsche Bank and Capital One, seeking documents related to loans he received.

In both cases, Trump said the subpoenas are invalid because they lack a “legitimate legislative purpose” — that is, they’re not tied to pending legislation. The argument is that Congress should not investigate the president’s conduct; that’s a job for prosecutors.

“A congressional demand for the President’s personal records raises the specter that members of the Legislative Branch are impermissibly attempting to interfere with or harass the Head of the Executive Branch,” according to a Justice Department brief filed at the U.S. Court of Appeals for the D.C. Circuit as part of the case involving Mazars USA.

In that filing, Justice Department attorneys echoed arguments made by Trump’s privately paid attorneys. They said Congress “may not issue a subpoena for purposes of ‘law enforcement.’ ”

So far, federal judges have rejected Trump’s argument.

“Congress plainly views itself as having sweeping authority to investigate illegal conduct of a President, before and after taking office,” U.S. District Judge Amit Mehta wrote in Washington in refusing to block the House subpoena for Trump’s accounting firm records. “This court is not prepared to roll back the tide of history.”

But the cases aren’t over. The subpoenas are on hold. In both cases, Trump appealed his losses to federal circuit courts.

The Justice Department also advised the Treasury Department to refuse a request from the House Ways and Means Committee to inspect Trump’s tax returns. The law says the returns must be turned over when requested.

But the Justice Department still said no: Its reasoning was again that there was no “legitimate legislative purpose” behind the request, so it was not valid. Democrats have sued to get the returns, and that case is still pending.

In the Manhattan district attorney suit, Trump’s private attorneys have turned their arguments from those other lawsuits inside out. Before, they said Congress should not obtain Trump’s records because that job was reserved for prosecutors.

In this separate case, Trump’s private attorneys have said prosecutors shouldn’t obtain them. That job, they said, was reserved for Congress.

“The Framers eliminated this possibility, and assigned the task to … Congress” by creating the impeachment process, Trump’s private attorneys wrote. They asked a judge to stop the subpoena: “Because [Vance’s] subpoena attempts to criminally investigate a sitting president, it is unconstitutional.”

Vance’s investigation is focused on hush-money payments made just before the 2016 election to two women who said they had sexual encounters with Trump. He has denied having relationships with the women.

Trump’s former attorney and “fixer,” Michael Cohen, pleaded guilty to campaign-finance violations for helping arrange those payments. Cohen said he’d been reimbursed by the Trump Organization. Federal prosecutors later effectively concluded their investigation without charging anyone else at the company.

After that, Vance’s office — which has the power to bring charges in New York state courts — began asking for documents related to the payments, as well as seeking tax returns for Trump and his businesses from Mazars.

Vance has rejected Trump’s arguments, saying the president is seeking to “invent and enforce a new presidential ‘tax return privilege’ ” that would bar anyone from seeing his returns. “No such privilege exists in the law,” Vance’s office wrote.

The Justice Department’s filing in the case doesn’t explicitly support Trump’s assertion of immunity from investigation. Instead, it urges District Judge Victor Marrero to slow the case down, keep the subpoenas on hold and listen carefully to Trump’s arguments.

Vance’s office has said the Justice Department is overstepping its bounds, and infringing on “the State’s sovereign right to enforce its criminal laws free from federal interference.”

Legal experts have said Trump’s arguments are a sharp departure from existing precedent: In the 1970s, for instance, the Supreme Court ruled unanimously that President Nixon had to turn over Oval Office tape recordings sought by prosecutors.

“What [Trump is] asking for, it seems implicitly, is for lower federal courts to ignore U.S. v. Nixon, or ultimately for the Supreme Court to overrule U.S. v. Nixon,” said Jed Shugerman, a law professor at Fordham University.

In his lawsuit against Vance, Trump cited a 2018 blog post written by Shugerman — quoting a line saying that presidents can’t do their job well if they’re being prosecuted.

But Shugerman said Trump is misconstruing his argument. He believes presidents shouldn’t be prosecuted while in office — hauled out of Washington and into a courtroom. But Shugerman said that doesn’t mean presidents can’t be investigated, for possible prosecution after they leave office.

If presidents can’t even be investigated, he said, that might incentivize them toward worse behavior.

“It creates a perverse incentive for a president to then break more laws to get reelected,” since the president would face no investigation for those, either, Shugerman said. “It gives him carte blanche as long as he wins two terms.”