Thank you for that excellent question. Actually, as my biography indicates, one of my articles is about that and is available online. You can read it there.
The short answer is no, we don't have a covenant, because a covenant implies a permanent commitment, and there has been no government that I know of that's prepared to make a permanent financial commitment to our veterans.
In 1938, the second-biggest budget item, next to paying off the interest on the national debt, was veterans' pensions. The public was outraged because it was in the middle of a depression, and people said, “Why are we paying so much to veterans?” Seventy percent of them were suffering from shell shock.
You have to remember that the public doesn't always support veterans, but there's a lot of support now. I would say that if we have anything, we have a social contract. The contract is negotiable using the government, the legislative process, and whatever financial means are available.