Cite as: 588 U. S. ____ (2019) 25 Opinion of the Court points during their lifetimes. For all of those reasons, asking judges to predict how a particular districting map will perform in future elections risks basing constitutional holdings on unstable ground outside judicial expertise. It is hard to see what the District Court’s third prong— providing the defendant an opportunity to show that the discriminatory effects were due to a “legitimate redistricting objective”—adds to the inquiry. 318 F. Supp. 3d, at 861. The first prong already requires the plaintiff to prove that partisan advantage predominates. Asking whether a legitimate purpose other than partisanship was the motivation for a particular districting map just restates the question. B The District Courts also found partisan gerrymandering claims justiciable under the First Amendment, coalescing around a basic three-part test: proof of intent to burden individuals based on their voting history or party affiliation; an actual burden on political speech or associational rights; and a causal link between the invidious intent and actual burden. See Common Cause, 318 F. Supp. 3d, at 929; Benisek, 348 F. Supp. 3d, at 522. Both District Courts concluded that the districting plans at issue violated the plaintiffs’ First Amendment right to association. The District Court in North Carolina relied on testimony that, after the 2016 Plan was put in place, the plaintiffs faced “difficulty raising money, attracting candidates, and mobilizing voters to support the political causes and issues such Plaintiffs sought to advance.” 318 F. Supp. 3d, at 932. Similarly, the District Court in Maryland examined testimony that “revealed a lack of enthusiasm, indifference to voting, a sense of disenfranchisement, a sense of disconnection, and confusion,” and concluded that Republicans in the Sixth District “were burdened in fundraising, attracting volunteers, campaigning, and generating inter-