The U.S. Congress Should Invoke the War Powers Act of 1973

In 1973, Congress ended funding for the [Vietnam] war in Indochina and, over President Richard Nixon's veto, passed the War Powers Resolution.

The resolution requires the president to notify lawmakers within 48 hours of sending armed forces into "hostilities" and to "terminate" such operations within a maximum of 90 days unless Congress specifically authorizes the deployment.  (Wall Street Journal)