My main man at Clemson, Bill Dougan, and I had a paper in the Journal of Law and Economics in 1989, entitled "The Rationality of Ideology".
We tried to think of examples that our theory would explain, examples that standard rational choice theory might miss. We thought of some.
But here is a terrific one:
"Republican House staff members who are losing their jobs in the aftermath
of November's loss of control are hoping Democrats will re-extend the hand
of largesse to them next month. As the old Congress wound down in a scramble
of post-election activity, incoming House Speaker Nancy Pelosi offered to
pay two months' severance to staff members working on some committees and in
House leadership offices. But her offer was scuttled - by Republican
lawmakers, who complained they didn't have the opportunity to study the
proposal and look at costs. The Senate already provides two months pay for
displaced staff members. One of the affected House staffers said his
comrades are mystified that a plan that would benefit employees of
Republicans would be killed by Republicans: 'We hope the Democrats revisit
it.'" [Wall Street Journal]
Now, that does NOT explain why these same yo-yos voted FOR all those roads bills, and earmarks. But the point is that the only way to establish an ideological reputation is when it costs you to do so.
(Nod to KL, who is neither rational nor ideological)