Republican Sen. Ron Johnson on Tuesday blocked a vote on the nomination of Deborah E. Lipstadt as the Biden administration’s antisemitism envoy. Instead Johnson met with a group of truckers in Washington, D.C., in protest of the COVID-19 mandates and to support those imprisoned for participating in the Jan. 6 assault on the Capitol.

Jewish groups expressed outrage at the holdup, with Anti-Defamation League CEO Jonathan Greenblatt calling Johnson’s behavior “disgraceful.”

The Senate Foreign Relations Committee was scheduled to vote to advance Lipstadt’s confirmation, one of about a dozen nominations, following a long-delayed and contentious hearing last month.

During the hearing Johnson accused Lipstadt, one of the foremost historians of the Holocaust, of engaging in the “malicious poison” of hatred for a tweet in which she accused him of engaging in white supremacy for his comments about the Jan. 6 riot. While Lipstadt expressed regret for the tweet, saying it was not meant as a personal or political attack, the Republican senator from Wisconsin indicated he would try to foil her nomination.