In an unexpected twist in President Donald Trump’s recent scandal involving Stephanie Clifford, the pornographic film star known as Stormy Daniels, the signature Mr Trump failed to place on Ms Clifford’s non-disclosure deal two years ago could play a decisive role.

If her lawyer has his way, there is a chance that the inch-long blank space could force President Trump to testify about what he knew of the arrangement.

The man who structured the hush-money payment, Mr Trump’s former lawyer and fixer, Michael Cohen, pleaded guilty to several charges in federal court.

Under the arrangement, Ms Clifford was paid $130,000 (£100,800) just before the 2016 elections to not speak publicly about an affair that she said she had with Trump.

In admitting to the scheme, Michael Cohen not only implicated himself, but also possibly his former boss, in a violation of federal campaign-finance law.

It remains unclear, however, whether Mr Trump, as president, can be held accountable for that offence.

That is where the missing signature comes in.

This year, Ms Clifford’s lawyer, Michael Avenatti, filed a lawsuit against President Trump and Mr Cohen, claiming that the non-disclosure contract was “null and void” because Mr Trump left empty the line where he was meant to write his name.

The lawsuit was stayed this spring after federal agents raided Cohen’s office and apartment, prompting him to invoke his Fifth Amendment right against self-incrimination to avoid having to testify in the suit. A federal judge agreed that if Cohen became a witness in the lawsuit, he could expose himself to legal risks in the FBI’s investigation.

The whole thing might have been dismissed as just another publicity stunt from Mr Avenatti, who has a penchant for making provocative statements about President Trump and who has even mused about running for president in 2020.

But now that Cohen has pleaded guilty, he may no longer be able — or choose — to avail himself of the Fifth Amendment’s safeguards.

Trump's presidency: US media reacts to Manafort and Cohen convictions Show all 16 1 /16 Trump's presidency: US media reacts to Manafort and Cohen convictions Trump's presidency: US media reacts to Manafort and Cohen convictions New York Post Trump's presidency: US media reacts to Manafort and Cohen convictions The Washington Post Trump's presidency: US media reacts to Manafort and Cohen convictions Newsday Trump's presidency: US media reacts to Manafort and Cohen convictions St Louis Post Dispatch Trump's presidency: US media reacts to Manafort and Cohen convictions Chicago Sun Times Trump's presidency: US media reacts to Manafort and Cohen convictions The Star Ledger Trump's presidency: US media reacts to Manafort and Cohen convictions Daily News Trump's presidency: US media reacts to Manafort and Cohen convictions The New York Times Trump's presidency: US media reacts to Manafort and Cohen convictions San Francisco Chronicle Trump's presidency: US media reacts to Manafort and Cohen convictions The Boston Globe Trump's presidency: US media reacts to Manafort and Cohen convictions Houston Chronicle Trump's presidency: US media reacts to Manafort and Cohen convictions Miami Herald Trump's presidency: US media reacts to Manafort and Cohen convictions Detroit Free Press Trump's presidency: US media reacts to Manafort and Cohen convictions The Wall Street Journal Trump's presidency: US media reacts to Manafort and Cohen convictions The Dallas Morning News Trump's presidency: US media reacts to Manafort and Cohen convictions USA Today

Because of that development, Mr Avenatti vowed last week to ask the judge to lift the stay and to let him question President Trump about Ms Clifford by taking his deposition.

“The developments of today will permit us to have the stay lifted in the civil case & should also permit us to proceed with an expedited deposition of Mr Trump under oath about what he knew, when he knew it, and what he did about it,” Mr Avenatti wrote on Twitter on the day Cohen pleaded guilty.

“We will disclose it all to the public.”

The legal manoeuvre arguably remains something of a long shot for Mr Avenatti.

Still, if he is eventually permitted to depose President Trump, he could direct his enquiries towards several unanswered questions that have lingered at the heart of the hush-money arrangement:

Was Cohen indeed reimbursed, as prosecutors claim, by the Trump Organisation? Which executives there were involved in the transaction? Was the payment made, as Cohen noted in his guilty plea, to influence the election?

The non-disclosure agreement silencing Ms Clifford was dated 28 October 2016, and was meant to be signed by four people: her first lawyer, Keith Davidson; Cohen; Ms Clifford herself (who was identified as “Peggy Peterson”); and Mr Trump (who was identified as “David Dennison.”)

While it may be curious that Mr Trump never signed the deal, the omission squares with his latest explanation for his role in the imbroglio.

After denying for months that he slept with — or paid — Ms Clifford, the president said last week that even though he was the source of the money, Cohen struck the deal without his knowledge and that he learned about it only after it was written.

Charles Harder, a lawyer representing Mr Trump in the lawsuit, did not return phone calls seeking comment.

Legal experts were divided about whether the missing signature was sufficient legal ground to take Mr Trump’s deposition.

“This is exactly the kind thing that Avenatti can take a deposition about,” said Debra Katz, an employment and whistleblower lawyer based in Washington who has negotiated several non-disclosure deals. “Because there’s no criminal case pending now and Cohen is out of jeopardy, it would be appropriate for the court to lift the stay and let the case go forward.”

But Douglas Wigdor, a New York lawyer who has represented several people — some with non-disclosure deals — who have sued Fox News for sexual harassment, said it was unlikely that the president could be deposed.

First, Mr Wigdor said, Cohen could ask for the stay to remain in place because his guilty plea does not immunise him from other potential charges, and he could thus still invoke his Fifth Amendment rights.

It also often happens, Mr Wigdor said, that executives of companies are sued, and the companies themselves negotiate the deals and pay the settlements without the executives ever being involved.

As long as Ms Clifford was paid, Mr Wigdor added, “Trump could have known or not known — signed or not signed — it doesn’t matter.”

Wigdor pointed out that a separate lawsuit that Mr Avenatti filed in June, accusing Cohen and Mr Davidson of colluding to quash Ms Clifford’s tale of an affair with Mr Trump, stood a better chance of resulting in depositions.

If it could be proved, Mr Wigdor said, that the two lawyers did collude with one another — especially for President Trump’s benefit — then Mr Avenatti would have “a stronger argument” for asking President Trump what he knew about the deal.

Dolores Troiani, a lawyer who helped Andrea Constand overcome a non-disclosure agreement to testify against Bill Cosby, leading to his sexual-assault conviction this year, suggested that the smartest move for Mr Trump and his team would be to nullify Ms Clifford’s contract on their own.

The president could be deposed, Ms Troiani said, only if he continues seeking to enforce the deal.

“If there is no contract, then no one is breach of it — and it’s done,” she said. “My advice? Just let it go.”