President-elect Donald Trump said he will act with “historic speed and strength” to fix the country’s problems as soon as he takes office Monday. “We have to do it. We’re not going to have a country left,” Mr. Trump said during his Victory Rally on Sunday at the Capital One Arena in Washington. “Before even taking office, you are already seeing results that nobody expected to see,” he said, adding that the changes are being called “the Trump effect.” “Since the election the stock market has surged and small business optimism has soared a record 41 points to a 39-year...