(Bloomberg) -- With the S&P 500 Index coming off its best stretch in nearly four decades, the road gets tougher for investors as the calendar flips to February — historically one of the rockiest times of the year for US stocks.Most Read from BloombergMusk Took Drugs With Some Tesla Board Members, WSJ SaysIraq Says 16 Killed in US Strikes, Calls Security Risk GraveBiden Swipes at Trump’s Personality in ‘Weirdest Campaign’ YetJapan Assures Fans Taylor Swift Can Make It to the Super BowlAfter a tor