Case: 21-51178 Document: 00516474571 Page: 11 Date Filed: 09/16/2022 No. 21-51178 Act” must “establish that no set of circumstances exists under which the Act would be valid.” United States v. Salerno, 481 U.S. 739, 745 (1987); see also Americans for Prosperity Found. v. Bonta, 141 S. Ct. 2373, 2387 (2021). “Such a challenge is the most difficult to mount successfully.” City of El Cenizo v. Texas, 890 F.3d 164, 187 (5th Cir. 2018) (quotation omitted). The Platforms do not even try to show that HB 20 is “unconstitutional in all of its applications.” Wash. State Grange, 552 U.S. at 449. 4 Instead, their challenge is premised on First Amendment overbreadth doctrine. Under this doctrine, the Supreme Court has “recognized a second type of facial challenge, whereby a law may be invalidated as overbroad if a substantial number of its applications are unconstitutional, judged in relation to the statute’s plainly legitimate sweep.” Bonta, 141 S. Ct. at 2387 (quotation omitted). This doctrine is limited to “the First Amendment context.” Ibid. “Overbreadth is a judicially created doctrine designed to prevent the chilling of protected expression.” Massachusetts v. Oakes, 491 U.S. 576, 584 (1989) (plurality op.); see generally Lewis D. Sargentich, Note, The First Amendment Overbreadth Doctrine, 83 Harv. L. Rev. 844 (1970). As the seminal case explained, the overbreadth doctrine addresses “threat[s] to censure comments on matters of public concern.” Thornhill v. Alabama, 310 U.S. 88, 97 (1940). The doctrine’s rationale is that “[m]any persons, rather than undertake the considerable burden (and sometimes risk) of vindicating their rights through case-by-case litigation, will choose simply to abstain from protected speech—harming not only themselves but society as a whole, 4 For example, the Platforms do not argue that HB 20’s provision restricting censorship based on “a user’s geographic location in [Texas]” could not be constitutionally applied to them. Tex. Civ. Prac. & Rem. Code § 143A.002(a)(3). While they vigorously argue that viewpoint-based censorship is protected speech, they nowhere contend that the First Amendment protects censorship based on geographic location. 11