There's nothing in the Constitution that demands the President of the United States obtains congressional approval before launching any military operation
Representative Dan Goldman (D-NY) screamed that, “Trump’s unilateral operation last night was an illegal act of war without Congress’s authorization.”
Representative Jim McGovern (D-MA) accused, “Without authorization from Congress, and with the vast majority of Americans opposed to military action, Trump just launched an unjustified, illegal strike on Venezuela.”
“President Trump’s unilateral military action to attack another country and seize Maduro, no matter how terrible a dictator he is, is unconstitutional and threatens to drag the U.S. into further conflicts in the region,” argued Senator Elizabeth Warren (D-MA).
Senator Ruben Gallego (D-AZ) also accused President Trump of illegal war activities, saying, “This war is illegal, it’s embarrassing that we went from the world cop to the world bully in less than one year.”
Except, there is nothing in the Constitution that demands the President of the United States obtains congressional approval before launching any military operation
The common argument claiming that Congress must approve any military operation is typically pulled from Article I, Section 8: “The Congress shall have Power…To declare War.”
Waging war and declaring war are two different authorities. By establishing the President of the United States as “Commander in Chief,” the President was given the authority to wage war when he feels it is necessary. In the Articles of Confederation, the two war powers (wage war and declare war) were established as separate powers, but both were given to the Congress of the Confederation because the President did not possess executive power. He was simply the President of the Congress, serving in a legislative manner, and carrying out ceremonial duties that were mostly symbolic as head of state. But, the Founding Fathers realized that there were many flaws in that system, and that an energetic President was necessary.
It was a balancing act. They feared having a king or ruler who constantly made war, or was willing to use a standing army against the people, but they also realized that giving the President no power to operate unilaterally in certain situations was dangerous as well. The President must be able to operate without asking for permission from the legislature, yet the legislature needed to have authorities to rein in a President should he act in a manner contrary to the interests of the country.