A spate of major court rulings rejecting claims of executive privilege and other arguments by Donald Trump and his top allies are boosting investigations by the US justice department (DoJ) and a special Georgia grand jury into whether the former US president broke laws as he sought to overturn the 2020 election results.

Former prosecutors say the upshot of these court rulings is that key Trump backers and ex-administration lawyers – such as ex-chief of staff Mark Meadows and legal adviser John Eastman – can no longer stave off testifying before grand juries in DC and Georgia. They are wanted for questioning about their knowledge of – or active roles in – Trump’s crusade to stop Joe Biden from taking office by leveling false charges of fraud.

Due to a number of court decisions, Meadows, Eastman, Senator Lindsey Graham and others must testify before a special Georgia grand jury working with the Fulton county district attorney focused on the intense drive by Trump and top loyalists to pressure the Georgia secretary of state and other officials to thwart Biden’s victory there.

Similarly, court rulings have meant that top Trump lawyers such as former White House counsel Pat Cipollone, who opposed Trump’s zealous drive to overturn the 2020 election, had to testify without invoking executive privilege before a DC grand jury investigating Trump’s efforts to block Congress from certifying Biden’s election victory.

On another legal front, some high level courts have ruled adversely for Trump regarding the hundreds of classified documents he took to his Florida resort Mar-a-Lago when he left office, thus helping an inquiry into whether he broke laws by holding onto papers that should have been sent to the National Archives.

“Trump’s multipronged efforts to keep former advisers from testifying or providing documents to federal and state grand juries, as well as the January 6 committee, has met with repeated failure as judge after judge has rejected his legal arguments,” ex-justice department prosecutor Michael Zeldin told the Guardian. “Obtaining this testimony is a critical step, perhaps the last step, before state and federal prosecutors determine whether the former president should be indicted … It allows prosecutors for the first time to question these witnesses about their direct conversations with the former president.”

Other ex-justice lawyers agree that Trump’s legal plight has now grown due to the key court rulings.

“Favorable rulings by judges on issues like executive privilege and the crime-fraud exception to the attorney-client privilege bode well for agencies investigating Trump,” said Barbara McQuade, a former US attorney for eastern Michigan. “Legal challenges may create delay, but on the merits, with rare exception, judges are consistently ruling against him.”

Although Trump has been irked by the spate of court rulings against him and his allies, experts point out that they have included decisions from typically conservative courts, as well as ones with more liberal leanings.

Former federal prosecutor Dennis Aftergut, for instance, said that: “Just last month, the 11th circuit court of appeals, one of the country’s most conservative federal courts, delivered key rulings in both the Fulton county and DoJ Trump investigations.”

Specifically, the court in separate rulings gave a green light to “DoJ criminal lawyers to review the seized, classified documents that Trump took to Mar-a-Lago, reversing renegade district court judge Aileen Cannon’s freeze-in-place order”, Aftergut said.

In the other ruling, the court held that Graham “couldn’t hide behind the constitution’s ‘speech and debate’ clause to avoid testifying before the Atlanta grand jury”, Aftergut noted.

“The speech and debate clause,” he pointed out, “only affords immunities from testifying about matters relating to congressional speeches and duties. That dog didn’t hunt here.”

Soon after these rulings, the supreme court left both orders in place. “It’s enough to make an old prosecutor with stubborn faith in the courts proud,” Aftergut said.

Separately, federal court judge David Carter, who issued a scathing decision earlier this year that implicated Trump and Eastman in a conspiracy to overturn the 2020 election, last month ruled that Eastman had to turn over 33 documents to the House January 6 panel including a number that the judge ruled were exempt from attorney-client privilege because they involved a crime or an attempted crime.

Ex-justice lawyers say that a number of the recent court rulings should prove helpful to the special counsel Jack Smith, who attorney general Merrick Garland recently tapped to oversee both DoJ’s investigation into Trump’s retention of sensitive documents post presidency and the inquiry into his efforts to stop Biden from taking office.

True to form, Trump didn’t waste any time attacking the new special counsel.

“I have been going through this for six years – for six years I have been going through this, and I am not going to go through it any more,” Trump told Fox News Digital in an interview the same day Smith was appointed. “And I hope the Republicans have the courage to fight this.”

Trump’s predictable pique notwithstanding, ex-prosecutors note that the court rulings that are proving beneficial to federal and state inquiries have largely come in response to lawsuits filed by Trump and key allies.

“The irony is that the new momentum has been spurred by lawsuits that Trump and his key loyalists filed as they’ve sought to block subpoenas for their testimony and documents,” Aftergut said.

The result, he added, is that multiple court rulings “are bound to have heartened those investigating Trump”.

What’s more, two lengthy reports in November by the Brookings Institution and Just Security that focused, respectively, on the Fulton county probe, and DoJ’s inquiry into Trump’s stashing of classified documents at Mar-a-Lago, presented strong evidence about the mounting legal threats Trump faces.

Now some former prosecutors sound bullish that charges against Trump involving one or more of the federal and state investigations are coming.

“I think Trump is likely to be charged in Georgia and in the documents case,” Michael Bromwich, an ex inspector general at DoJ, told the Guardian. “I’ll be interested to see which happens first.”