What would be some public arguments, campaigns, or products that might and might not benefit from Colin Powell's endorsement?
To answer this, you need to think about what sorts of groups would have positive attitudes towards Colin Powell and what groups would have negative attitudes or would not really know who he is. You then need to think about what products or campaigns would be trying to target those people.
Perhaps the two most important things about Powell in this context are that A) he was a highly respected military man and B) he was best known quite some time ago. Therefore, his endorsement would be useful for products that have an older and somewhat more conservative target audience. For example, he would not be useful for a cutting edge technology aimed at younger people. He might be better for something like an insurance company or a credit card like American Express that is aimed at an older demographic and whose target market would respond to someone older with a very dignified reputation.