If I'm reading the Pew article correctly, Methodists, Episcopalians, Presbyterians, Lutherans, Catholics and Jews are over-represented in Congress in comparison to their percentage of the population.  Baptists, Nondenominational Protestants, Pentecostals, Adventists, Buddhists, Muslims, Hindus and nones are underrepresented. While nones are the most underrepresented, Pentecostals are very underrepresented as well (.4% of Congress, 5% of the population).

I can see why nones and non-Christians are underrepresented. I wonder what accounts for the underrepresentation of nondenominational Protestants and Pentecostals.