Newt can speak to issues in a more professorial, academic way.
Cain can manage an organization and execute.
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In that position, he led the house to several major victories, and also some failures. But he was clearly a leader who could persuade others to do his bidding.
Cain was a middle manager who was good at cost-cutting and problem solving. He was appointed to run a small subsidiary of Pillsbury that they had obtained in a multi-million dollar deal, a subsidiary worth possibly $150 million.
He abandoned a growth policy, and adopted a slash-and-hold strategy, cutting all franchises that were not profitable. He also cut the management staff, although in a smaller proportion to the number of franchises they had left to manage. By favoring immediate returns over growth, he managed to turn a small loss into an even smaller profit, around $2 million, or about 1% gross margin.
After the two+ years he worked to turn it around for Pillsbury, they gave up and sold the company at a loss to Cain, for somewhere between $30 million and $100 million.
He then managed the company for 8 more years, competently keeping the company at a steady earnings rate, while not growing at all. Other pizza companies took a more agressive policy, and Godfather's went from the 5th largest company to the 8th largest. He remained on the board for a half-dozen more years -- when he left, they were the 11th-largest.
Yes, he can manage an organization, and execute. In Godfather's, he had complete control of the company. He had to reach no consensus, he would make a decision and people would execute it. It is a totally different thing than being a governor, or a president, where you have to build consensus and cajole people into doing your bidding.
There is no evidence that Cain has that kind of leadership qualities. Time and again this election cycle he has gone off half-cocked, making declaratory statements without getting the facts, and looking foolish. It's just a campaign, so he was able to correct his statements each time, eventually.
But as President, you make a decision and things happen. If you mistakenly conclude that a country was behind a terror attack, and you send in the marines, it's not enough to send out your campaign chief to blame the internet for giving you the wrong information.