There's Mainstream Today: "As Tuesday's elections showed, support for limited government remains a mainstream position," writes Quin Hillyer at American Spectator. This is the socio-political mainstream, and it can vary with time and place.
And There's Mainstream Forever: As the Declaration, Constitution, and Bill of Rights show, support for limited government under God is the mainstream American position. This is the foundational, enduring meaning of the American mainstream, and it liberates across time and place precisely because its meaning is secure.
To the degree that a president or political party advocates a vision or policy outside of the abiding meaning of the American mainstream, to that degree a president or party is moving away from the genius of the American experiment.
At present, the liberal Democratic Party is outside of the socio-political mainstream and far outside of -- and even against -- the enduring American mainstream. Thus its extremism on both accounts. Thus its increasing embrace of tyranny, from the womb to the marketplace, against speech and family, and on and on.
The Republican Party is a house divided and for this reason totters. Party elites seek the sociological mainstream but reject the enduring American mainstream. Even with bombast, they speak weakly and carry a small stick.
The hope of America is that the mainstream of today embraces the mainstream that endures. That happened once and lasted a while. Maybe it can happen again.
* March 27, 2010, Update: For a treatment of this topic in light of the tea parties, town halls, and so on, please see, "How the New Resistance Can Win the Culture War," published at WorldNetDaily and The Pearcey Report (updated 9.21.10).