For seven years Fox News has pushed back against the daily scrutiny and criticism leveled at it by Media Matters, the liberal watchdog group. But after David Brock, the group’s founder, said in March that his group’s new strategy amounted to a “war on Fox,” Fox ratcheted up its response. In the past ten days, the news channel has run more than 30 segments calling for the nonprofit group to be stripped of its tax-exempt status. Its Fox Nation website has even provided a link to pre-completed complaint forms