Robert Kagan at The Washington Post:
In recent decades, however, party loyalty has superseded branch loyalty, and never more so than in the Trump era. As the two Trump impeachments showed, if members of Congress are willing to defend or ignore the president’s actions simply because he is their party leader, then conviction and removal become all but impossible. In such circumstances, the Framers left no other check against usurpation by the executive — except (small-r) republican virtue.
Critics and supporters alike have consistently failed to recognize what a unique figure Trump is in American history. Because his followers share fundamentally conservative views, many see Trump as merely the continuation, and perhaps the logical culmination, of the Reagan Revolution. This is a mistake: Although most Trump supporters are or have become Republicans, they hold a set of beliefs that were not necessarily shared by all Republicans. Some Trump supporters are former Democrats and independents. In fact, the passions that animate the Trump movement are as old as the republic and have found a home in both parties at one time or another.