Here and here.

Because Louisiana simultaneously submitted this plan to DOJ, and filed for preclearance in federal court, the state runs the risk of having an objection interposed before the court can take up the issue.  If that happens, as a practical matter, it will taint the court’s view of the plan. The state could always withdraw the objection before DOJ gets a chance to interpose an objection.  Even a DOJ request for more information could gum up the court process.