In June of 1971, which event increased the credibility gap and anti war protests?

The massacre of civilians at My Lai

The killing of four students at Kent State University

The leaking of the pentagon papers to the press

The bombing of Viet cong bases in Cambodia

The answer is The massacre of civilians at My Lai.

My Lai was a place in Vietnam where it was believed to be a stronghold of the country. Military US troops had a mission in this area but they found out that the South Vietnam Army was not there. Being high on drugs and heroin, the US army was no longer in their right thinking and created a massacre mostly of women, children and the elderly were the victims. The news was tried to be prevented, however, it came to the US and the people condemned and protested about this occurrence.