You can read the brief here. (Texas redistricting has all the amicus briefs filed so far here.)  As I expected, DOJ (and soon the respondents) make much of the D.C. Circuit’s recent opinion denying preclearance of the underlying plans.  From the DOJ brief:

Here, by contrast, Texas has not been found tocarry its burden under Section 5, even in part. BecauseTexas elected to forgo administrative preclearance, the Attorney General has not been given the opportunity toobject (whether to certain districts, as in Upham, or more broadly). And the D.C. district court has not held in Texas’s favor on either prong of Section 5. To the contrary, the D.C. district court has unanimously denied Texas’s motion for summary judgment and found suffi-cient evidence of invidious purpose and retrogressive effect to warrant a trial. See p. 6,supra

.The evidence of invidious purpose (see p. 6,supra ) is particularly significant. The State acted in ways consis-tent with a focus on race, and the outcome of that race-focused process was a significantly discriminatory effect on minority voters–not just in particular districts but as a whole.  Compare Upham, 456 U.S. at 40 (requiring deference only as to particular districts as to which there was no “constitutional or statutory violation”). For instance, while minorities accounted for most of Texas’s population growth, none of Texas’s new congressional seats was drawn in a way that could augment minorities’ voting power.  The D.C. district court agreed that the government’s evidence to that effect could “provide significant circumstantial evidence” of discriminatory purpose.