Look at your second source. Look at the "not a mistake" percentage start out at 59% in 1965 and slowly walk down to around 40% in 1968 and then around 30% in mid-1971. The "was a mistake" crowd starts at 25% and over the same period walks up to 60%. i.e. it began with domestic popularity, as all US-promoted wars tend to, whip the libs up to fight the enemy, and then deteriorated as consequences built up. Then new narratives were created to cope with this reality. Much like with Iraq, many were apparently always against the war even though a couple years earlier they cheered on the cops against protesters. No concern for the much larger numbers of Vietnamese and Cambodians killed and injured really registered among the US masses, of course, despite the efforts of left organizers. That was never considered a mistake and still isn't among Americans.
Regarding your first source, it is basically irrelevant. What Americans now think about the US war on Vietnam is entirely propaganda narrative.
There is nothing in "the data" contrary to what I said. Would you like to explain what is liberal about the basic realities of history and explaining your own sources back to you?
This is why kkkrackers are so sensitive about the price of eggs