Most important, the interdependency doctrine helps Obama paint his policies as part of a unified vision rather than a set of unrelated ideas. Compare his web of interwoven policies—the stimulus, health care, efficiency standards, the auto bailout—with George W. Bush's legislative patchwork. Bush did not lack for vision. Many of his policy goals, such as invading Iraq and privatizing Social Security, were part of a larger narrative of "expanding freedom." But others, such as No Child Left Behind and the expansion of Medicare, were stand-alones. He didn't try to fit them into a story.
Obama's hardly the first person to use the technique. When Franklin Delano Roosevelt was selling the New Deal, everything was billed as helping the economy, from ending Prohibition to subsidizing art projects. During World War II, many domestic policies were geared toward winning the war. Americans were even urged to grow "victory gardens" in their backyards to reduce the price of food for troops, and to buy war bonds. Since then, every president from Kennedy to Clinton has described their policies as somehow interdependent, part of a larger agenda. (For example, welfare reform, the Brady Bill extending waiting periods on handgun purchases, and reducing the deficit all fell within Clinton's rubric of personal responsibility.)
But Obama has done it most effectively. One reason may be his background. As someone born in Hawaii, raised in Hawaii and Indonesia, and educated mostly in the Northeast—and who has family in Kenya—he speaks with some authority about how political and cultural shifts in the United States affect the rest of the world. And it helps that modern technology has made those shifts both more swift and more obvious.
But perhaps the biggest reason Obama can squeeze everything into one narrative is, ironically, the economic collapse. As he noted in his Cairo speech, the financial crisis reminded everyone just how codependent we are: "For we have learned from recent experience that when a financial system weakens in one country, prosperity is hurt everywhere." That lesson has driven the administration's thinking on a lot more than just the economy. When Chief of Staff Rahm Emanuel said the Obama administration should see the economic crisis as an opportunity, he presumably meant that it would allow Congress to pass laws that would not have been possible otherwise. What he probably didn't realize is that the economic crisis would color the administration's entire worldview.
Of course, there's a downside to all this conditionality. Linking policies to one another is effective when you're trying to shove a lot of bills through the door at once, as Obama is. In that case, you can plausibly say, Pass them all, or the whole structure will collapse. It's less effective when you have to pick and choose. In addition, it's often useful for a politician to be able to compartmentalize issues: OK, forget about Wall Street regulation for now. How about health care? Arguing that everything is related—that one policy's success depends on that of another—may make it harder to peel off supporters for specific issues. It also risks alienating allies who aren't onboard for the entire Obamagenda.
It's inevitable that Obama will have to start the process of disconnecting. So far, however, he hasn't had to decide which parts of his agenda to jettison. (Immigration reform was on its way to getting punted; then it wasn't.) So for now, he gets to seem coherent and visionary. Americans understand better what their government is trying to accomplish—even if they don't agree. And with a public insurance option, we prevent the next 9/11.