ExxonMobil fired back at government accusations that it covered up the issue of climate change, claiming the U.S. Virgin Islands' attorney general targeted it in an unconstitutional "fishing" expedition…ExxonMobil sued Virgin Islands Attorney General Claude Earl Walker, the Cohen Milstein Sellers & Toll law firm and attorney Linda Singer on Wednesday in Tarrant County Court.  ExxonMobil says Walker issued a subpoena in March under the U.S. territory's anti-racketeering law that is "little more than a weak pretext for an unlawful exercise" of power. It says the "chilling effect" of the subpoena's demand for internal documents "strikes at protected speech at the core of the First Amendment." ExxonMobil's lawsuit appears to be the first of many in the fight over climate change as it cites the "Green 20" group of attorneys general who announced one week after the subpoena that they will "com[e] up with creative ways to enforce laws being flouted by the fossil fuel industry."