As gay people around the country reveled on Sunday in the historic Senate vote to repeal “don’t ask, don’t tell,” a liberal media watchdog group said it planned to announce on Monday that it was setting up a “communications war room for gay equality” in an effort to win the movement’s next and biggest battle: for a right to same-sex marriage. The new group, Equality Matters, grew out of Media Matters, an organization backed by wealthy liberal donors — including prominent gay philanthropists — that has staked its claim in Washington punditry with aggressive attacks on Fox News and conservative...