This was very much expected. But it's also very much an election-year gift to Republican Attorney General (and gubernatorial candidate) Rob McKenna:

Today Backpage.com LLC brought suit in the United States District Court for the Western District of Washington against Attorney General Rob McKenna and the state’s county prosecutors. The suit seeks a Declaratory Judgment that a new Washington law, Senate Bill 6251 (“SB 6251”), is invalid, and asks for a Permanent Injunction against enforcement of the law. Backpage.com also filed a motion that requests enforcement of SB 6251 be prevented pending a decision by the Court on the merits of the challenge to the law.

McKenna has lately been talking a lot about his campaign against underage sex trafficking, and the fact that he's now being taken to federal court by the owners of Backpage.com, whom he describes as a huge part of this country's underage sex trafficking problem, will I'm sure come up at least few times on the campaign trail as the fall approaches.

But political implications aside, this suit could force an answer to interesting questions about just how much leeway people like McKenna—and Democratic State Senator Jeanne Kohl-Welles, sponsor of SB 6251, and Seattle Mayor Mike McGinn, who joined Kohl-Welles today in saying once again that Backpage "facilitates the exploitation of minors in cities and towns across America"— actually have to punish the site.

At issue, at least according to Liz McDougall, general counsel for Village Voice Media Holdings, LLC (owner of, among other things, Backpage.com and The Seattle Weekly), is respect for the First Amendment, the Fifth Amendment, the Commerce Clause, and the federal Communications Decency Act.

Washington State's effort to punish "online service providers" (like, say, Backpage) for "misuse of the Internet by third parties" (like, say, people who place ads for underage sex workers on Backpage) runs afoul of all of these legal limitations, McDougall claims.

We'll see if the federal courts agree. Meanwhile, McDougall is asking the federal court system for suspension of—and "a permanent injunction against the enforcement of"—SB 6251. (Documents here, here, and here.) And McGinn and Kohl-Welles are asking, in a statement: "How long will Village Voice Media continue to choose profits over protecting children?”