Maybe someone can help me out here. I have been looking for a chart that provides a quick comparison of countries like the US, Ireland, Portugal, Greece, Italy, etc. to get a better understanding of why a particular country gets in trouble (pretty much every EU country listed) with rating agencies and another (the US) doesn't.
There is some material out there, such as the chart to the left from here, showing that the US is one of the worst performers according to a single parameter (national governmental debt per capita in euros – the figure reportedly rises to around 250,000 euros per capita if we include debt at all levels of government and include private debt [see the second chart below from here]), but part of the problem is that the criteria on which the three major rating agencies, all of which are based in New York City incidentally, are not actually known, so it would be hard to come up with an exhaustive chart.
It is worth keeping in mind an article from the Washington Post from 2004, which essentially describes these rating agencies as a kind of mafia. They go door to door to companies offering to give them a free rating along with a request that the company should pay for these ratings at some point in the future. If the company repeatedly refuses to pay, the rating agency goes into full-attack mode and severely downgrades the company's stock. Such attacks are especially egregious when the rating agency that the company actually pays continues to give the firm a good rating.