President Trump, who has mastered the 24-hour cable news cycle and social media like no other president, bashed Comcast Corp. on Saturday in two tweets that called Comcast-owned news channels MSNBC and NBC purveyors of fake news on the Mexican border crisis. But then Trump courted the Comcast media empire on Monday by calling into CNBC and using it as a bully pulpit to put pressure on the Federal Reserve to cut interest rates and to encourage China to make a deal on tariffs.