House Democrats plan to make Donald Trump's alleged involvement in a 2016 scheme to silence two women who claimed they had affairs with him a major investigative focus this fall, picking up where federal prosecutors left off in a case legal experts say could have led to additional indictments.

The House Judiciary Committee is preparing to hold hearings and call witnesses involved in hush-money payments to ex-Playboy model Karen McDougal and adult-film actress Stormy Daniels as soon as October, according to people familiar with the plans who spoke on the condition of anonymity to describe internal discussions.

Democrats say they believe there is already enough evidence to name Trump as a co-conspirator in the episode that resulted in his former attorney Michael Cohen pleading guilty to two campaign-finance charges.

Cohen, who is serving a three-year prison sentence for those counts and other crimes, testified under oath that Mr Trump directed the payments that helped land him behind bars. Federal prosecutors in Manhattan also described Mr Trump's alleged role in the scheme, referring to him in court papers as "Individual-1."

But they concluded their investigation this summer without bringing any additional charges.

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The hush-money inquiry will open a new chapter in the House's months-long consideration of whether to draft articles of impeachment against the president.

The new congressional inquiry will reopen questions about the extent of Trump's involvement in the episode – and whether he would have been charged if not for Justice Department opinions that a sitting president cannot be indicted.

"The fingerprints are all over this one – it's not like a big mystery," said Jamie Raskin, a member of the Judiciary panel. "As with the evidence of presidential obstruction of justice, the conclusion seems inescapable: that [Trump] would have been tried had he been anybody else. And now it's left to Congress again to figure out what to do with the lawbreaking and apparent impunity of the president."

Mr Trump, his aides and attorneys have made contradictory statements about the president's knowledge of the payments. But his lawyers have repeatedly denied that Mr Trump committed wrongdoing.

"No campaign violations were engaged in by the president," said Jay Sekulow, Mr Trump's personal attorney.

As part of the probe, Democrats plan to explore whether the investigation was stymied or obstructed. The Judiciary Committee is also considering as a potential witness David Pecker, the chairman and CEO of American Media Inc., the parent company of The National Enquirer, which admitted making the payment to McDougal.

AMI complied with a document request Democrats made earlier this year, giving the committee all communications it previously turned over to law enforcement, according to the people familiar with the inquiry.

A lawyer for Mr Pecker, Elkan Abramowitz, declined to comment. AMI declined to comment.

Stormy Daniels claims she had sex with Trump, and alleges she was paid hush money during the 2016 election (Getty Images)

The conclusion of the campaign-finance investigation this summer surprised some former federal prosecutors and legal experts, who noted that other participants in the scheme were granted immunity or non-prosecution agreements, which often signal that the case is focused on additional targets.

"It's inconceivable Michael Cohen acted alone ... what happened?" said Duncan Levin, a former prosecutor for the Justice Department and Manhattan district attorney's office. "When you have one of the most important, sensitive investigations into the president and his family and his company, and then when you unexpectedly drop it, it is going to raise a lot of questions."

A Justice Department spokesman in Washington referred questions to the US attorney's office of the Southern District of New York, which declined to comment.

It remains to be seen how far congressional Democrats will be able to get in their inquiry. Mr Trump and his administration have succeeded in blocking many of the House oversight investigations, refusing to provide information and challenging subpoenas in court.

When the House returns to session next week, the Judiciary panel plans to continue focusing on five episodes of potential obstruction of justice by the president outlined in special counsel Robert Mueller's lengthy report this spring. Democrats have argued that Trump would have been charged with obstruction in those five instances were he not president.

The hush-money payments represent a sixth instance of potentially impeachable presidential misbehaviour, they say.

The scheme began in the final months of the 2016 campaign, when Cohen has said there was building fear in Trump's inner circle that Ms McDougal and Ms Daniels would go public with allegations that they had sexual encounters with Mr Trump years earlier.

Cohen told prosecutors that "in coordination with and at the direction" of Mr Trump, he worked with Mr Pecker to pay $150,000 (£125,000) to Ms McDougal as part of a "catch and kill" operation. He also said he worked "in coordination" with the then-GOP presidential candidate to arrange a $130,000 (£108,000) payment to Ms Daniels, whose real name is Stephanie Clifford.

Mr Trump and his aides initially denied knowing about the payments – and then offered shifting explanations for their purpose.

"We have no knowledge of any of this," spokeswoman Hope Hicks said in November 2016, after The Wall Street Journal reported on the payment to Ms McDougal.

After The Journal reported on the existence of the Stormy Daniels payment early last year, a reporter on Air Force One asked the president: "Did you know about the $130,000 payment to Stormy Daniels?"

"No," Mr Trump responded.

"Then why did Michael Cohen make [the payment], if there was no truth to her allegations?" a reporter asked.

"You'll have to ask Michael Cohen," Mr Trump said.

The following month, however, Mr Trump attorney Rudy Giuliani said that the president reimbursed Cohen for the $130,000 paid to Ms Daniels, adding that Mr Trump "didn't know about the specifics of it, as far as I know."

But Cohen said in federal court and before Congress that Mr Trump directed the payments.

In testimony before the House Oversight Committee in February, Cohen said Mr Trump had assured him in an Oval Office meeting that he would take care of Cohen's debt related to Ms Daniels, which Cohen had financed through a line of credit.

Former Playboy model Karen McDougal claimed she had an affair with Trump

Cohen displayed what he said were reimbursement checks for the $130,000 payment to Ms Daniels – one dated August 1, 2017, which he said was signed by the president; the other from March 17, 2017, which he said was signed by Donald Trump Jr., the president's son, and Allen Weisselberg, the Trump Organisation's chief financial officer

"I am going to jail in part because of my decision to help Mr Trump hide that payment from the American people before they voted a few days later," he said.

Federal prosecutors also implicated Mr Trump in the alleged hush-money scheme, noting in court filings before Cohen's sentencing that the former Mr Trump lawyer "admitted, with respect to both payments, he acted in coordination with and at the direction of Individual-1," a reference to the president.

The payments essentially functioned as in-kind donations to Mr Trump's presidential campaign, prosecutors said. The money paid to Ms McDougal by National Enquirer parent company AMI violated a ban on corporate contributions, while the money that Cohen directed to Daniels constituted an excessive campaign contribution, they alleged.

Prosecutors also released a non-prosecution agreement struck with AMI, in which the company said it knowingly acted "in concert" with Mr Trump's campaign to silence the women and did not notify the Federal Election Commission of the election-related payments.

Michael Cohen has 'more information' on Trump, lawyer says

Prosecutors said AMI officials knew "expenditures by corporations, made for purposes of influencing an election and in coordination with or at the request of a candidate or campaign, are unlawful," the agreement said.

The document acknowledged that AMI's main purpose was "to suppress the model's story so as to prevent it from influencing the election," the agreement said.

As part of the deal, AMI agreed to cooperate with any law enforcement agency pursuing the matter and to train executives and editorial employees on election laws and their application to media operations.

In addition, federal prosecutors secured the cooperation of Mr Weisselberg, who testified before a grand jury. But no further charges were filed.

In July, the federal judge supervising the case, William Pauley, said "the government has effectively concluded its investigations" of who besides Cohen was involved.

The Manhattan district attorney picked up an aspect of the case, issuing subpoenas in August to the Trump Organisation about the money paid to Ms Daniels as part of an inquiry into whether the Trump Organisation falsified business records.

A lawyer for the Trump Organisation, Alan Futerfas, declined to comment.

It remains unknown whether federal prosecutors would have sought to charge Mr Trump if not for Justice Department legal opinions concluding that indicting a sitting president could interfere with the office's unique constitutional responsibilities.

In part because of those opinions, Mueller decided that he could not even consider whether to charge Mr Trump in his obstruction-of-justice inquiry.

New York University law professor Stephen Gillers called it "troublesome" that the campaign-finance case ended without providing more answers, arguing that "it would disserve the public interest if the Justice Department did not eventually disclose who else was party to Michael Cohen's crime."

"There is clear evidence that one or more people participated in Cohen's crime," he said. "We just don't know who they are and whether they are subject to investigation and could still be prosecuted."

Karl Sandstrom, a former member of the Federal Election Commission, said that based on his review of the matter, prosecutors in Manhattan had an "exceedingly strong case." He questioned why they did not pursue others involved.

"They saw fit to put Michael Cohen in jail," he said. "Why aren't the people who authorised and paid for this culpable?"

In announcing the conclusion of investigation, Judge Pauley immediately released documents that had been under seal, saying every citizen should have "an opportunity to scrutinise the materials" in a case of "national importance."

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House Democrats saw his comments as an indication that they should pick up the investigation, according to aides familiar with their investigative plans.

The Judiciary Committee is now eyeing Pecker and AMI as potential sources of new information. The panel this summer authorised subpoenas for Pecker, a close Mr Trump confidant for years, and National Enquirer editor Dylan Howard, who also cooperated with federal prosecutors.

Documents released by Mr Pauley show that after The Washington Post published a recording in October 2016 in which Mr Trump bragged about groping women, Cohen exchanged "a series" of messages and calls with Pecker, Howard, Trump and Daniels's attorney, among others.

The documents included notes of an FBI agent that stated, "based on the timing of these calls, and the content of the text messages and emails, I believe that at least some of these communications concerned the need to prevent Clifford from going public."

As part of the probe, Democrats are expected to put a spotlight on Mr Trump's evolving explanations about what he knew of the scheme, according to the people familiar with the strategy. They also hope to review a Justice Department decision to end the hush-money query by pressing Barr about it directly in a future hearing.