Stock futures backed off Monday, with the Dow industrials threatening to snap a four-day run-up, as investors awaited details on a $908 billion federal pandemic relief package. Some chipmakers and oil producers came under early pressure. Moderna led a jump among coronavirus vaccine stocks, as the first doses of the Pfizer/BioNTech vaccine were set for roll out in the U.K. Boeing jumped after the 737 Max’s first passenger-carrying flight in 22 months.