Political analyst Mark Shields, best known for his decadeslong stint on “PBS NewsHour,” died Saturday at his home in Maryland. Shields was 85. His daughter, Amy Shields Doyle, told the New York Times the cause was complications of kidney failure. Judy Woodruff, the anchor and managing editor of “NewsHour,” confirmed his death in a tweet that also praised his “encyclopedic knowledge of American politics, his sense of humor and mainly his big heart.” “I am heartbroken,” she said. Shields, a native of Weymouth, Massachusetts, graduated from the University of Notre Dame in 1959 and then went on to…