Diplomats and international lawyers like to settle disputes without the use of force. Military operations often have unintended consequences and unpredictable results. Diplomats, however, need more than persuasive arguments; they need incentives and leverage to get results. Thus, they want to back diplomatic activities with the threat of force, in order to make agreement now preferable to conflict.
In U.S. military parlance, the tools to back diplomacy are called "flexible deterrent options," FDOs. That's what we're seeing now in areas near Iran, according to the New York Times. The United States is deploying ships and aircraft that could be used for military action,offensive or defensive. I hope they won't be needed, but I believe that their presence may help convince Iranian leaders that we mean what we say and have "options on the table" that they would find less acceptable than a solid international agreement.
Such actions are also clearly within presidential war powers --provided they don't include secret kinetic operations that make combat more likely.