Maybe your being a Canadian is getting in the way of fully appreciating the American conditions, but to speak of the "relations between the secular and religious left" or to say that "[p]rogressive clergy and church people have always been an important part of the left" obscures the American problem: in the USA, there is NO mass institution on the Left that is largely made up of secular leftists. NONE.
One, we do not have a mass social democratic party; two, most Democratic voters are religious; most trade unionists are also religious. A tiny minority of secular leftists belong to this or that miniature socialist sect, and most secular leftists are loose canons who do not have any enduring mass institution they can call their secular leftist base.
In short, the only organized mass institutions on the broadly defined Left are (1) explicitly religious institutions and (2) secular institutions that are largely composed of religious individuals in the USA. That's the American point of departure, a unique point of departure among the industrial nations. -- Yoshie <http://montages.blogspot.com/> <http://mrzine.org> <http://monthlyreview.org/>