Over the past few months, at least 100,000 Russian troops have assembled next to that country’s western border with Ukraine — a chilling and unprecedented scene not witnessed since Moscow annexed Crimea in 2014. Some international observers have pointed to it as Putin’s posturing and a means to chest thump at the new Biden administration. Others have expressed deeper concerns that it is the start of another plan to seize Ukrainian territory. But what remains indisputable to many analysts is Washington must not look weak in this ongoing watershed moment, which could ultimately set th...