Even when the president gets consent of Congress, it doesn't safeguard against anything. They can be deceived too.
http://www.nytimes.com/2010/07/15/world/asia/15vietnam.html?_r=0
For sure the Gulf of Tonkin incident has been showing up on more conspiracy threads than history threads in recent years. Which probably inspired the NY Times reporter to look into it.
But I am quite certain that neither Lyndon Johnson nor anybody in Congress ever even considered that Vietnam would escalate to the decade of massive bloody mess it became. Any more than President Bush or the Congress ever envisioned that Vietnam or Iraq would turn out the way they have. In all these cases they expected limited military action to get an enemy to back off, cease, desist, and be no trouble to us thereafter. Sometimes our military ventures turn out that way. But it didn't turn out that way in Vietnam, in Afghanistan, or in Iraq. And in all cases when we choose to just stop fighting a war instead of winning a war, we leave perpetual enemies in our wake.
One of the traits of a Republic is that the people will support righteous retribution when warranted, but they also will quickly become war weary. The American people are currently very war weary.
But we have a President who doesn't seem to notice and who may or may not care about that. And who may or may not exercise the judgment that most of us would consider good judgment.
And he has full power to order military action that could result in our getting involved in another perpetual war at any time.