But by Friday evening, with the White House and Congress in turmoil and two Republican members of the Judiciary Committee, Senators Mike Lee of Utah and Thom Tillis of North Carolina, among those announcing they had tested positive for the virus, it was clear that the challenge had grown steeper.

Top Republicans insisted they would move ahead at an uncommonly swift pace to hold hearings on Judge Barrett’s nomination by Oct. 12, send her nomination to the full Senate by Oct. 22 and confirm her as soon as Oct. 26, eight days before Election Day — even if it meant breaking Senate norms and considering a lifetime judicial nomination by videoconference.