What was the main factor in the decline of the Great Society?

The consensus among historians is that the Vietnam War
killed the Great Society.

When Pres. Lyndon B. Johnson
pledged to create a "great society" and to wage a "war on poverty," it was clear that
these goals would take a huge amount of spending on the part of the government.  If the
government was going to be able to commit this kind of money to fighting poverty, it had
to avoid excessive spending in other areas.

This was not to
be.  As Johnson's presidency went on, the war in Vietnam expanded and became more
expensive.  As this happened, it became harder and harder for the government to afford
all of the programs of the Great Society.   In addition, the problems of Vietnam helped
force Johnson to forego running for reelection in
1968.

Between the lack of money and the fact that a
Republican, Richard Nixon, was elected in 1968, the Great Society was doomed. 
Therefore, most historians say the Great Society's decline was caused by the Vietnam
War.