During the Vietnam Era, could a president have been elected who did not have a strong anti-communist stance?
No president in the entire Cold War era could have been elected without being relatively anti-communist. There could be differences between presidents who would favor a more aggressive approach to the Soviets and ones who favored a less aggressive approach, but all presidents had to be anti-communist.
If anyone had tried to run for president on the platform of true peace with the Soviets, they would not have been able to win. Americans were very suspicious of Soviet power and Soviet motives. They believed that it was important to do things like expanding American involvement in Vietnam (as Johnson did) because they believed that the Soviets would try to expand their power and that such expansion would hurt the US.
It would not have been possible to elect a president in this era who actually felt the US should not try to resist communism vigorously.