It is extraordinarily difficult to believe that Madison could have understood the Establishment Clause as creating a wall of separation that would prohibit (or disfavor) the very political activity that had enabled him to win election, serve in the First Congress, and argue for adoption of the Establishment Clause; that is, Leland’s political activity in his role as a religious leader, political activity that had been crucial to giving Madison the opportunity to be in Congress and to propose the Bill of Rights. In fact, Leland remained a staunch Jeffersonian Republican (and, later, a Jacksonian Democrat) his entire life and continued to use his religious influence as a very popular Baptist preacher to advance that party’s cause—apparently without any objection from Jefferson, Madison, Monroe, Jackson, or Van Buren—until his death in 1841.
At the very least, Leland’s role in furthering the proposal of the Bill of Rights casts doubt on any approach to the Establishment Clause that would limit or discourage participation by religious leaders and religious communities in the political arena.
From John Leland and James Madison: Religious Influence on the Ratification of the Constitution and on the Proposal of the Bill of Rights by Mark S. Scarberry, Professor of Law, Pepperdine University School of Law.
You can read the complete essay here.