Isn't any undeclared war unconstitutional?
All Congress had to do was declare war.
Of course not.
Just because Congress has constitutional authority to formally declare a state of war between the US and another sovereign nation does not mean that the Executive's ability to render aid to our allies or undertake police actions is limited.
The Constitution guarantees the Executive complete authority over the deployment of US armed forces abroad.
Of course, if he wants money to fund his deployments, he needs Congress to write him a check.