As President-elect Joe Biden prepares to take office in January, much of what he can accomplish depends heavily on the partisan makeup in Washington. The key issue for the broader U.S. economy in the near term is the prospect of further federal fiscal stimulus designed to offset the effects of the coronavirus pandemic. Reports that at least two experimental vaccines are highly effective and might gain initial approval by year-end may give the new administration a leg up in battling the health and economic crisis—and could be the most important factor for longer-term growth.