WASHINGTON (Reuters) – The impeachment inquiry into U.S. President Donald Trump’s dealings with Ukraine takes a major step forward on Wednesday when the Democratic-led House of Representatives Judiciary Committee has its first hearing to consider possible charges against the Republican president. Here are some facts about the hearing: WHO WILL TESTIFY? The House Judiciary Committee is charged with deciding whether to recommend articles of impeachment against Trump to the full House. The panel’s chairman, Democratic Representative Jerrold Nadler, will preside over an expected series of hearings. Lawmakers will hear testimony from four law professors on what constitutes an impeachable offense. The U.S. Constitution says broadly that these are “high crimes and misdemeanors” committed by presidents and other government officials. The witnesses are: Noah Feldman, professor of law at Harvard Law School; Pamela Karlan, professor of public interest law at Stanford Law School; Michael Gerhardt, professor of jurisprudence at the University of North Carolina School of Law; and Jonathan Turley, professor of public interest law at the George Washington University Law School. Turley is the lone Republican witness. QUESTIONING OF WITNESSES When the hearing begins, Nadler and the committee’s top Republican, Doug Collins, are expected to make opening statements and allow each witness to do the same. Then the questioning begins. Under the committee’s impeachment inquiry procedures, Nadler and Collins can conduct 90-minute rounds of questioning, alternating sides every 45 minutes. Nadler and Collins will likely give part of their time to committee lawyers. Once these rounds of questioning end, each lawmaker will get to ask questions for five minutes. WHAT HAPPENS NEXT? The committee is expected to hold more proceedings, including a hearing to examine the findings of impeachment investigators led by the House Intelligence Committee. But no further sessions have yet been scheduled. Any articles of impeachment recommended by the committee would be sent to the full House for a vote, which could happen by the end of the year. Any trial would take place in the Senate, which is controlled by Trump’s Republican party.