Since the launch of his political career more than a decade ago, President Donald Trump has always been sensitive to his approval ratings. His popularity in office has never topped 50 percent, a first for a modern president, but there has also consistently been a clear floor: Despite numerous scandals and unpopular political positions, Trump’s support has remained above 35 percent in most polls—and more often than not, above 40 percent—throughout his first and second terms.But as Trump’s war on...