It has long been the case that neither U.S. major party could claim a large enough percentage of the electorate's loyalty to win a Presidential election with its own voters alone. Seldom will one party's nominee have enough appeal to members of the other party to make attracting sizable numbers of them a likely-winning strategy. It has long been the idea of both parties' operatives, therefore, to attract other voters — moderate or centrist voters — in order to have a winning number of electoral votes for their respective tickets. In order to do this, candidates generally feel compelled to modify positions taken in order to secure the support of enough of the base voters of their own party to secure its nomination in the first place. The term "Vital Center" can be said to have two meanings — "vital" in the sense of necessary or essential for winning, and "vital" in the sense of "living", for the attempt to capture it often seemingly breathes new life into ideas that have been figuratively carved into stone by partisan supporters.
The Vital Center will likely remain such as long as the majority of Americans do not strongly identify with all the major ideas of either major party, which increasingly seems to be the case. For example, most reliable polling data seems to indicate that a vast majority of Americans as a whole do not support amending the United States Constitution to make almost all abortions illegal. But the same polling also indicates that most Americans do not regard the right to abortion under almost any and all circumstances to be an inalienable right akin to free speech or freedom of religion. Likewise, most Americans believe in the right to own and possess firearms, but do not see that this right is somehow diminished or eliminated by some governmental regulations designed to keep automatic weapons, or weapons that can easily be converted into automatic weapons, out of the hands of private individuals. As long as the two major parties take positions which are out of touch with most Americans in order to please their most ardent advocates and supporters, they will find themselves scrambling for votes in the center in order to achieve a winning margin.