At the NATO summit in Brussels, President Joe Biden must not mistake smiles for commitments.

The summit offers an important opportunity, indeed a responsibility, for Biden to outline America’s expectation that true alliances require fair burden-sharing. He will rightly reaffirm the U.S. commitment to NATO’s Article 5 mutual defense stipulation, but he must also explain why the alliance is not currently credible as a deterrent against prospective enemies such as Vladimir Putin’s Russia.