What granted the US president broad military powers in Vietnam?

The Gulf of Tonkin Resolution in 1964 gave U.S. President Johnson any military force necessary to protect U.S. interests. The "War Powers Resolution" in 1973, which over-rode President Nixon's veto, restricted the President's power, without "Congressional Approval." The WPR was brought about by President Nixon's ground campaigns in Cambodia & Laos in 1970 and 1971, respectively.