The department said in a statement that it was “shifting these matters to a new team of Civil Division lawyers going forward.” It offered no explanation for the en masse change, which came on the heels of an extraordinary week in a yearlong clash over the issue that has raised concerns about whether the department’s arguments for adding the question could be believed.

And it strongly suggested that the department’s career lawyers had decided to quit a case that at the least seemed to lack a legal basis, and at most left them defending statements that could well turn out to be untrue.

“There is no reason they would be taken off that case unless they saw what was coming down the road and said, ‘I won’t sign my name to that,’” Justin Levitt, a former senior official in the Justice Department under President Barack Obama, said on Sunday.