More often than not, Republicans who sell themselves to voters by invoking conservative principles wind up catching Potomac fever once they arrive in Washington--think Orrin Hatch, Marco Rubio, Jeff Flake, and so on.
Sometime in the mid 1990s, he fell in love with Bill Clinton and decided being the "gentleman of the U.S. Senate" was more important than representing his constituents.
Helms was one of a handful who held his ground until the day he retired.