Not all military actions require Congressional approval.
Going to Congress takes some time, and so you don’t always have that time.
I don’t think that case law has precisely hammered out the division at the level of the US Constitution, but in legal terms, a major element is the War Powers Resolution:
en.wikipedia.org/wiki/War_Powers_Resolution
The War Powers Resolution (also known as the War Powers Resolution of 1973 or the War Powers Act) (50 U.S.C. ch. 33) is a federal law intended to check the U.S. president’s power to commit the United States to an armed conflict without the consent of the U.S. Congress. The resolution was adopted in the form of a United States congressional joint resolution. It provides that the president can send the U.S. Armed Forces into action abroad only by Congress’s “statutory authorization”, or in case of “a national emergency created by attack upon the United States, its territories or possessions, or its armed forces”.
The bill was introduced by Clement Zablocki, a Democratic congressman representing Wisconsin’s 4th district. The bill had bipartisan support and was co-sponsored by a number of U.S. military veterans.[1] The War Powers Resolution requires the president to notify Congress within 48 hours of committing armed forces to military action and forbids armed forces from remaining for more than 60 days, with a further 30-day withdrawal period, without congressional authorization for use of military force (AUMF) or a declaration of war by the United States. The resolution was passed by two-thirds each of the House and Senate, overriding the veto of President Richard Nixon.
In practice, the US has not declared war since World War II, though it has engaged in many military conflicts since then. What has happened, for major conflicts, is that Congress has passed some form of military authorization permitting continued combat operations in line with the above act.
In part, I believe it was the practical pressures of the nuclear weapons era that gave the President more freedom to act. There would be no time to obtain approval from Congress in a number of nuclear weapons scenarios, and if you let the Executive make use of the nuclear arsenal — a really big stick — without Congress’s approval, it seems a bit odd to restrict use of conventional force.
I also suspect that one factor is that war is also politically risky; if it becomes unpopular, a Congressman — who may be around for a lot longer than a President, who will be out after two terms — may not want to have a declaration of that unpopular war on his record, and would prefer to minimize involvement, so Congress is generally not, for political reasons, adverse to reducing its exposure.
The issue here is that there’s a certain assumption in that legislation that the freedom given the President is because he requires a great deal of leeway to respond rapidly to unexpected dangers.
In this case, that wasn’t the case, though I suspect one could make a fair argument that an operation of the sort taken required operational secrecy, and Congressional debate would be at serious odds with it.
I think that it’s fair to say that the US has taken the position some time before now that ejecting Maduro is okay and a goal — that’s why Venezuela has been under the sanctions, for example, to create political pressure. That hasn’t worked. The question is really whether that policy can or should be shifted from economic pressure to military force.