You mean since the founding of the republic? http://www.businessinsider.com/american-presidents-republica.... George Washington was worth an estimated $500 million. Adams was a pauper at only $20 million. Jefferson was $200m+ before he went broke. Madison was $100m+.
The average net worth of senators is skewed up by a few wealthy businessmen. The median is around $2.5 million, which is actually not even top 1%. The top 5% mark is at $1.8m. And don't forget: Senators skew married, skew older, skew white, skew educated relative to overall households, and all of those characteristics are correlated with higher income and net worth. The median senator might not even crack the top 5% if you look only at households with white married 60-year olds who all have college degrees and 60% of whom have a JD or MD.
$2.5 million net worth is rich, but it's not "plutocracy" rich. It's "two Google engineers marrying and buying a house and putting money into their 401ks for 30 years" rich.