Larry Kudlow, President Trump’s top economic adviser, suffered a heart attack on Monday evening and was at Walter Reed Medical Center, Mr. Trump said in a tweet. Mr. Kudlow, 70, who has referred to himself as a “happy warrior” in counseling Mr. Trump on trade and economic policy, joined Mr. Trump’s team in March as the director of the National Economic Council. “Our Great Larry Kudlow, who has been working so hard on trade and the economy, has just suffered a heart attack. He is now in Walter Reed Medical Center,” Mr. Trump tweeted, just before a meeting in Singapore...