Richard Lugar, John Warner, Lincoln Chafee, Mike DeWine, John McCain and Peter Fitzgerald failed to sponsor the Lawful Commerce in Firearms bill, i.e. the product liabilty wanted by the firearm manufacturers. Others accused of being RINOs include Arlen Spector, who has a primary challenge, Charles Grassley and Orin Hatch, but Hatch sponsored a bill to recognize gun rights in D.C.
IIRC, Chafee and Warner won elections in 2002. Warner had no rat opposition, IIRC, but this term may be his swan song. Fitzgerald is retiring this year, and maybe McCain might join him. AFAIK, McCain hasn't announced his intention. If he runs, I expect a primary challenge. I believe all the rest are safe this year.
McCain's running again. He waffled a little but then went for it. No serious primary challenge either; Rep. Jeff Flake looked at it but decided McCain would "whip him".