With respect to Mitt Romney personally, his descent from being a very decent, honorable man began years before he hit the national spotlight. I speak from personal knowledge. I don’t know that any one of them is different. Even Ron Paul appears to have succumbed to money-grubbing since his exit from elected politics in 2012, even if his message is generally what we might agree with.
"Ye hear of wars in far countries, and you say that there will soon be great wars in far countries, but ye know not the hearts of men in your own land."