Cite as: 581 U. S. ____ (2017) 3 Opinion of the Court or abridgement of the right . . . to vote on account of race.” §10301(a). We have construed that ban to extend to “vote dilution”—brought about, most relevantly here, by the “dispersal of [a group’s members] into districts in which they constitute an ineffective minority of voters.” Thorn­ burg v. Gingles, 478 U. S. 30, 46, n. 11 (1986). Section 5, at the time of the districting in dispute, worked through a different mechanism. Before this Court invalidated its coverage formula, see Shelby County v. Holder, 570 U. S. __ (2013), that section required certain jurisdictions (including various North Carolina counties) to pre-clear voting changes with the Department of Justice, so as to forestall “retrogression” in the ability of racial minorities to elect their preferred candidates, Beer v. United States, 425 U. S. 130, 141 (1976). When a State invokes the VRA to justify race-based districting, it must show (to meet the “narrow tailoring” requirement) that it had “a strong basis in evidence” for concluding that the statute required its action. Alabama Legislative Black Caucus v. Alabama, 575 U. S. ___, ___ (2015) (slip op., at 22). Or said otherwise, the State must establish that it had “good reasons” to think that it would transgress the Act if it did not draw race-based district lines. Ibid. That “strong basis” (or “good reasons”) standard gives States “breathing room” to adopt reasonable compliance measures that may prove, in perfect hindsight, not to have been needed. Bethune-Hill, 580 U. S., at ___ (slip op., at 16). A district court’s assessment of a districting plan, in accordance with the two-step inquiry just described, warrants significant deference on appeal to this Court.2 We of course retain full power to correct a court’s errors of law, —————— 2 Challenges to the constitutionality of congressional districts are heard by three-judge district courts, with a right of direct appeal to this Court. See 28 U. S. C. §§2284(a), 1253.