Chait counters Krugman:

It begins as a policy argument (we need more stimulus) which is true. But then it quickly acknowledges that Congress won't pass more stimulus, so it switches to a political argument (Obama should attack Congress for opposing more stimulus.)

So now we're not really arguing about what to do about the economy. We're arguing about political messaging. But it's pretty clear that the concept of economic stimulus is unpopular. People think it's a big waste of money. So what is the value of devoting a lot of presidential energy to an unpopular message? There's no real evidence that sustained presidential rhetoric can change people's minds on issues where they've formed an opinion.