Does the Constitution require a declaration of war for President Trump to maintain his Iran offensive?

When the Constitution was adopted, international law required declarations only for offensive, not defensive, conflicts.
United States v. Abbott and State War Powers

A federal court of appeals has upheld the right of Texas to defend itself against illegal immigration by erecting a barrier in the Rio Grande River.
Obama’s Libyan Operations are Unconstitutional
You can sympathize with the humanitarian motives of our Libyan intervention while still doubting its constitutionality. The Constitution prescribes the rules about how the United States is to enter a war, and the Obama administration has violated those rules. The administration argues that the hostilities, because limited, do not rise to the level of “war,” […]