The former Fox News host Tucker Carlson, declaring, “We’re back,” said on Tuesday that he was starting a new show on Twitter, a sign that negotiations to reach an amicable separation with the network, where he is still under contract, had broken down.Mr. Carlson offered no details of when his new program would begin or what kind of content it would have. The many unanswered questions highlighted the uncertainties surrounding his future — a career in which he would be deprived of a prime-time platform on Fox News.Among the possibilities: Fox could ultimately block any attempt by the host to return to a prominent role in conservative media.A representative for the Fox Corporation, which has been engaged …
