“The impetus for this is to start repairing the harm this administration has done to the federal bench,” Ms. Aron said of the new project.

The liberal groups also unhappily remember a relatively slow start to the judicial nominating process by Mr. Obama’s administration given its need to focus on the faltering economy and other issues. That forced the White House to try to make up ground later, only to run into a Republican-controlled Senate.

Unlike the unprecedented Trump list, the liberal groups do not intend to make their recommendations public — they see them more as a guide for a potential Democratic administration. The idea is to look at district and appellate courts that could experience a rush of retirements after the election and find suitable successors for anyone who leaves.

Those involved in the effort say a main focus will be on identifying potential candidates who could diversify the nominees for the federal bench beyond the usual categories of sitting judges, prosecutors and senior law partners — potentially including public defenders, civil rights advocates and others with more varied backgrounds.

“It would be nice to see more people who have experience outside the three big pots,” said Peter Shane, a constitutional law professor at Ohio State University and a member of the Building the Bench advisory committee.

Of course, there is no certainty that the veteran judges who had been placed on the bench by Democrats are interested in leaving. But politically strategic retirements are hardly unheard-of at either the Supreme Court or lower court level. It would only make sense that a judge would like a successor to share some common ground and legal view.

Just last week, Mr. McConnell said in a Fox News interview that he doubted any of the four members of the Supreme Court nominated by Democrats would quit the court while Mr. Trump was in the White House — outside of what Mr. McConnell called “a significant life-ending event.”