By Fareed Zakaria, CNN

If you think politics have heated up this summer, you ain't seen nothing yet. The presidential campaign is going to get underway in a serious way soon and expect it to get nasty.

I'm not making any assumptions about the Republican candidate and what he or she will say on the stump. I'm making this prediction because I think we're going to go into an election with a bad economy the likes of which we have rarely seen.

Take a look at the chart below. It shows American GDP trend growth over the last 125 years. Those red patches at the bottom are when we go below the long-term trend.

As you can see, we are now at the longest period of below-normal growth since the great depression. And it doesn't seem likely to pick up anytime soon.

Take a look at another chart, this one from an upcoming special we will be doing on jobs. This one tracks how fast job growth comes back after recessions. You can see, over the last ten years, a new pattern has emerged in the American economy - jobless growth.

Why is this happening? Well, we don't know for sure. Clearly the immediate cause is that we went through a massive bubble in housing which burst. Beyond that, we have gone through a period of about twenty-five years where we all accumulated too much debt - government and people - and we are going to have to start paying off that debt. History shows that this process of de-leveraging, as economists call it, makes it hard to grow fast.

We also have these two big forces - technological change and globalization –that encourage businesses to become much more efficient - and need fewer workers - and also gives them almost unlimited places where they can hire workers and set up new factories, often more cheaply than in the United States.

I know that these forces have been around for a while, but over the last 20 years they seem to have gathered enormous strength. All of which is to say, we're living through some very difficult challenges. No one - no one - has ready answers to them. But that will not stop politicians from demagoguing. So expect a pretty raucous election season.

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