Progressive groups are stepping up calls for Justice Stephen G. Breyer to “immediately” retire from the Supreme Court and allow President Biden to nominate a successor while Democrats control the Senate, which approves judicial nominees. In an advertisement to be released on Friday, 18 legal scholars will describe Justice Breyer as “a remarkable jurist” but say “it is time” for him to announce his retirement. Another advertisement — endorsed by 13 progressive groups, including Black Lives Matter, Women’s March and Battle Born Collective — was released on Wednesday.