Trump has all but stated this is for conveying 'strength' (my word). That DODefense conveys the US being the weaker state. Geez.
A "declaration of war" is a formal notification between states that a condition of war exisits. Must identify the enemy, the grievances, among other terms.
As mentioned, only Congress can "declare war" after a formal request from the President. Today, war can exist without a formal declaration. Following the Korean War, various 'authorizations' exist for deployments for military puroses.
AUMF, Authorizations for Use of Military Force. AUMFs by Congress were used for US involvement in:
*War in Vietnam (undeclared conflict authorized by Congress through the Gulf of Tonkin Resolution of 1964, giving LBJ authority to take military action).
*War in Afghanistan. Military action following 9/11. Bush. No formal declaration.
*War in Iraq. US lead invasion Operation Iraqi Freedom, Bush, concern over WMDs and terrorism. No formal declaration.
Before those:
*Korean War . No formal declaration. UN authorized Truman this "police action" to bypass need for Congressional declaration of war. **This set the framework for avoiding the legal and political implications of a formal declaration of war.
The last formal declaration was by FDR after Pearl Harbor attack by Japan, entered the US into WWII (already in motion among countries).
I didn't make any of this up, just looked it up.
But we all know all those wars and police actions and conflicts extended more significantly in length and loss of life than bargained for at their initiation, all in the name of "protection" of somebody. JMHO.
Candy