By Fareed Zakaria, CNN

I wrote a blog post for the Global Public Square website that has gotten a great deal of reaction. So let me talk about it for a moment.

It all started because I read a website that pointed out that after the S&P downgrade of the United States, no country with a presidential system has a AAA rating from all three major ratings agencies.

Only countries with parliamentary systems have that honor (with the possible exception of France, which has a parliament and prime minister as well as an empowered president).

This brought to mind my years in political science grad school and an essay by, a famous Yale scholar, who says that parliamentary systems are superior to presidential systems because they allow for greater stability and purposive action.

In a parliamentary system, he contended, the legislature and the executive are fused so there is no contest for national legitimacy.

Think of David Cameron in England. He is head of the coalition that won the election, head of the bloc that has a majority in parliament and head of the executive branch as Prime Minister.

Remember, the political battle surrounding the debt ceiling is actually impossible in a parliamentary system because the executive controls the legislature.

There could not be a public spectacle of the two branches of government squabbling and holding the country hostage.

In the American presidential system, in contrast, you have the presidency and the legislature, both of which claim to speak for the people.

As a result, you always have a contest over basic legitimacy. Who is actually speaking for and representing the people?

In America today, we take this struggle to an extreme. We have one party in one house of the legislature claiming to speak for the people because theirs was the most recent electoral victory.

And you have the president who claims a broader mandate as the only person elected by all the people.

These irresolvable claims invite struggle.

There are, of course, advantages to the American system - the checks and balances have been very useful on occasion. In 1945 Britain enacted a quasi-socialist economic plan that set the country on a bad path.

But look at the situation today. Western countries all have created welfare states and governmental systems that are cumbersome, sluggish and expensive –especially as the population ages.

These need to be reformed and many of the reforms are fairly obvious - in social security, energy policy, tax reform. But the American government has lost the ability to actually implement any policy solutions because of political gridlock

Listen to what the S&P actually said in its downgrade. "America's governance and policymaking [is] becoming less stable, less effective and less predictable than what we previously believed.. . Despite this year's wide-ranging debate, in our view, the differences between political parties have proven to be extraordinarily difficult to bridge."

This is not just about the presidential system alone. Recent developments have added to polarization and paralysis. The fillibuster for example, is not in the constitution but it is now routinely used to allow a minority of one house to block all legislation.

In a fast-moving world, where other countries are acting quickly and with foresight, we are paralyzed.

It's all very well to keep saying that we have the greatest system in the histroy of the world but against this background of dysfunction, it sounds a lot like thoughtless cheerleading.