For only the fourth time in U.S. history, the House of Representatives has started a presidential impeachment inquiry.

House committees are trying to determine whether President Donald Trump violated his oath of office by asking Ukraine to investigate political rival Joe Biden and his family and to investigate the country’s involvement in the 2016 U.S. presidential election.

House Republicans came forward Saturday with a list of witnesses they want the House Intelligence Committee to hear from during the public hearings, set to start this coming week.

Most prominent among them: the anonymous whistleblower and former U.S. vice-president Joe Biden’s son, Hunter. Majority Democrats are unlikely to approve the list as delivered. They’ve fought back Republican attempts to expose the identity of the whistleblower, whose complaint is at the heart of the impeachment effort.

Republicans are seeking testimony from eight specific witnesses as well from all officials, so far anonymous, who helped the whistleblower prepare the complaint.

U.S. House Intelligence Committee chairman Adam Schiff said three State Department witnesses will appear on Wednesday and Friday: the U.S. ambassador to Ukraine, Bill Taylor; career department official George Kent; and Marie Yovanovitch, the former U.S. ambassador to Ukraine.

Yovanovitch was ousted in May on Trump’s orders and Taylor replaced her; both have testified about their concerns with the administration’s policy on Ukraine. The committee also must consider whether to summon the witnesses sought by Republicans, who call the impeachment process a sham.

Trump is expected to address reporters at 12:30 p.m. ET on Saturday.