Trump is no more "waging war" on the media than he is on Russia.  He tweets those things precisely because they're outrageous.  It cements the deal with his base: he's outrageous in the defense of their resentments and insecurities, they exalt him as their hero.  Trump knows perfectly well that he can do nothing to abridge the freedom of American media.  The impossibility of it frees him from any responsibility for actually doing it; he'll blame the "inaction" on Congress.  The First Amendment has withstood attacks by many more tough and intelligent enemies than this buffoon.  A few of them were named John Adams (Alien and Sedition Acts), Abraham Lincoln (suspension of habeas corpus to permit military commanders to arrest seditious speakers and editors), and Woodrow Wilson (whose attorneys general prosecuted Eugene Debs for antiwar speeches and later sponsored the Red Scare of 1920, when hundreds of suspected "anarchists" and "radicals" were arrested).