In neither case was the opposition "suckered" into anything, any more than President Roosevelt "suckered" the Japanese into attacking Pearl Harbor.
By the way, just so we're clear on this: I believe and have for years argued on Free Republic, that President Roosevelt did, in effect, "sucker" the Japanese into attacking Pearl Harbor, because that was the only possible way to get the United States into WWII in time to save the Brits and any semblance of western civilization in Europe.
But "suckered" or "un-suckered" doesn't matter.
The facts are that the United States in 1941 committed no -- zero, zip, nada -- acts of war against Japan, while the Japanese attack did in fact create a state of war with the United States.
The same is true of Fort Sumter in 1861, except, except that there was no possible "suckering" involved, since Confederate President Davis had already ordered preparations to assault Sumter, even before Lincoln's inauguration!
Davis was prepared for, and threatened, military assault on Sumter -- a clear act of war against the United States -- regardless of what Lincoln had said or did.
Lincoln merely allowed Davis (as Roosevelt "allowed" the Japanese) to carry out military attacks, creating states of war, which Confederates (and Japanese) believed were absolutely necessary for their own survival.
So Sumter and Pearl Harbor started war, and all the rest -- including Unconditional Surrender -- necessarily followed.
As for Lyndon Johnson's Gulf of Tonkin Incident -- there was an actual incident, in which North Vietnamese forces did attack US Navy ships.
Also, "Suckered" or "un-suckered", North Vietnamese were in fact assaulting militarily their neighbors to the south and west, including US forces sent to help those people.
Indeed, by August of 1964, about 150 US military had already died, and hundreds more wounded, in the Vietnam conflict.
So Johnson's decision to request authorization for limited war was, he believed, both reasonable and necessary.
The veracity of reports from the Gulf of Tonkin were irrelevant to Johnson's, and even Congress's, overall thinking.
You know the difference between LIHOP and MIHOP, right?
LIHOP (Let It Happen On Purpose) takes a passive approach that encourages a path but does not insist upon it. It fertilizes the favored path and promotes a thing to occur.
MIHOP (Make It Happen On Purpose) takes a more hands-on approach, crafting the circumstances upon which others are forced to react to something you sparked - whether you do anything else or not.
With regard to FDR, I believe that he LIHOP. His intel told him of the massive buildup of the Japanese navy and the hardening of attitude towards the United States. His analysts told him that when the Japanese envoys suddenly turned gracious and conciliatory it was because they had internally decided that war was the only option - but did not wish to share that attitude with the Americans. FDR knew what was coming and did nothing because, as you said, “that was the only possible way to get the United States into WWII”.
The Lost Causers would have us believe that Lincoln LIHOP’ed the south - “suckered” them into attacking. That’s foolish on the face of it. Lincoln was overtaken by the events even before he could assume office. His response was methodically slow - hoping all along to draw the recalcitrant rebels back into the fold.
The enmity and hostility of the southern fire-eaters was well established. They had been agitating and creating discord among the states for a very long time. The notion of secession was not a spontaneous one. Rather, they looked for the right circumstances to make it happen on purpose - and then set it into motion.