Dan Quayle explains his endorsement of Mitt Romney in an op-ed in the Arizona Republic:
[Romney] has proven over and over again that he is a leader. He has demonstrated he is capable of making tough decisions and turning things around. He is a man of integrity. He understands budgets and financial markets. He balanced budgets and met a bottom line. He is strong on national defense and has a deep love of the principles that make America great.
Mitt Romney has what it takes to be a great president of the United States, and that is why I enthusiastically endorse him for president.
Full piece here.