Former Special Counsel Jack Smith appeared on Capitol Hill on Wednesday for a high-stakes, closed door hearing about his two defunct criminal investigations into President Donald Trump.

In his opening statement, he told Congress his team developed proof beyond a reasonable doubt that Trump engaged in a criminal scheme to overturn the 2020 election results. Smith also charged Trump for allegedly mishandling classified documents.

Trump pleaded not guilty in both cases, and the prosecutions ended after his re-election.

Since returning to office, Trump has demanded investigations of officials who criminally charged him.

House Judiciary Chairman Jim Jordan, a staunch Trump ally, called Smith's investigations partisan and politically motivated.

In an October letter to Smith, Jordan accused the career prosecutor of using disturbing tactics.

Republicans also expressed alarm at the decision to subpoena the phone records of several Republican lawmakers as part of his election investigation.

Smith is testifying in a closed setting on Wednesday, meaning that the public will not be able to hear from him in real time.

According to sections of his opening statement obtained by the BBC's US partner CBS News, Smith told lawmakers that in both of his investigations, the basis for those charges rests entirely with President Trump and his actions.

Smith also said the investigators found powerful evidence that Trump had retained classified documents and obstructed efforts to return them to the government.

He will likely face tough questions from the Republican-controlled committee, currently chaired by Jordan, a long-time Trump ally who was a staunch defender of the president during both of his impeachment inquiries.

Democrats on the panel said they wanted to learn more about the results of Smith's inquiries.

We want to hear exactly what he found, and what he did, Congressman Jamie Raskin the top House Judiciary Democrat, told Politico.

According to Smith's attorney Peter Koski, the special counsel had volunteered to testify in an open hearing.

Smith, was disappointed that offer was rejected, and that the American people will be denied the opportunity to hear directly from Jack on these topics, Koski told Politico earlier this month.

The stakes are high for Smith, who Trump has deemed a criminal and suggested should be investigated and put in prison along with other Department of Justice officials involved in the 2020 election inquiry.

In September, the Department of Justice indicted former FBI Director James Comey based on testimony he gave to Congress in 2019. In November, a federal judge tossed out the case after finding the prosecutor who brought it was improperly appointed.