I think malleable politicians are malleable because they try to benefit the largest section of the population that they can. Conservatives, lately, have focused on benefiting a very small segment of the population directly, expecting the benefits to trickle down.
However, the trickle down has not worked. I know very little about economics, but, I remember, headlines in newspapers eight years ago were mainly about unemployment, and the growth of the National debt. The euro was $1.30 (now it buoys around $1.10).
I think the American economy is much better now than it was eight years ago, and a larger section of the population has benefited from that, than when principled conservatives were in the government. (And this is just from an economic point of view, which is a small part of the benefits).
Would you rather have an ethically malleable liberal than a principled conservative? In most cases I would rather have the principled politician because they will have some kind of goal to benefit some segment of Americans. Can we really say that any ethically malleable politician, of any flavor, will always help some segment of Americans?
Then as a counter to all this. Nixon did found the EPA.