On Wednesday former U.S. Special Counsel Robert Mueller arrived on Capitol Hil to testify to lawmakers in two televised hearings.
Mueller, whose inquiry detailed extensive contacts between Trump's 2016 campaign and Russia at a time when Moscow was interfering in the 2016 election with hacking and propaganda, is set to appear in separate hearings before the House of Representatives Judiciary and Intelligence committees.
Democrats, who control the House, hope his testimony will rally public support behind their own ongoing investigations of the Republican president and his administration, even as they struggle with whether to launch the impeachment process set out in the U.S. Constitution for removing a president from office for "high crimes and misdemeanors." Mueller is not expected to deliver any new bombshells, according to Democratic aides, but rather stick to the contents of his 448-page investigation report about the 22-month-long probe of Russian election meddling.
Mueller plans to deliver an opening statement before taking questions.
Republicans are expected to object to the presence of Aaron Zebley, the former deputy special counsel who had day-to-day oversight of investigations in the inquiry, who will accompany Mueller.
Zebley will be present at the Judiciary hearing, according to Mueller's spokesman Jim Popkin and a House Judiciary staffer, and will be sworn in as a witness for the intelligence panel, according to an aide for that committee.
"This was specifically NOT agreed to," Trump wrote on Twitter on Wednesday morning before the hearing was set to begin.
Democrats hope the 74-year-old former FBI director will give the American public a compelling account of Russia's sweeping interference, the Trump campaign's readiness to accept help from Moscow and Trump's efforts to impede the Russia probe that Mueller investigated as potential obstruction of justice.
Trump, running for re-election in 2020, is hoping to move past the entire Russia issue.
Mueller's report said the investigation found insufficient evidence to prove that Trump and his campaign engaged in a criminal conspiracy with Russia.
The report also did not reach a conclusion on whether Trump committed the crime of obstruction of justice but pointedly did not exonerate him.
Attorney General William Barr, a Trump appointee, subsequently cleared the president of obstruction of justice.