If liberalsim has undermined America, why do we have steady economic growth throughout the 20th century?

if the cons hate liberalism, why don't they do away with the communist liberal protectionist trade policies America practices, despite losing cases in the international courts. it seems some liberalism is good for the cons if it puts more money in their pockets. alot of that steady growth is financed at 29% and your dollar is way over valued, true growth has happened, but we are seeing a slow down in this growth, not just a spike but a gradual slow down.