From the CNN/YouTube Democratic debate in Charleston, S.C., in July 2007: "I actually think that we should explore nuclear power as part of the energy mix. There are no silver bullets to this issue [of climate change]."

In the September 2007 MSNBC debate in New Hampshire: "I don't think that we can take nuclear power off the table. What we have to make sure of is that we have the capacity to store it properly and safely, and that we reduce whatever threats might come from terrorism."

In a town hall event in Iowa in December 2007: "I start off with the premise that nuclear energy is not optimal. I am not a nuclear energy proponent."

At a meeting with Democratic governors this week: "I've said this before, I don't think that nuclear power is a panacea. But I also think that given that it doesn't emit greenhouse gases, for us to invest some R&D into seeing whether we can store nuclear waste safely, or reuse it. These are all areas where the market interacting with a clear set of rules by the federal government and billions of dollars devoted to research and development can, I think, trigger the kind of economic growth that we haven't seen in this country for a long time."

This is certainly not the unflappable support for nuclear that we see from McCain, but does that mean it's flip-flopping? There's a consistent thread running through Obama's statements: a pragmatic recognition that nuclear power has problems (e.g., safety, waste storage), but that it's a part of the U.S. energy mix that doesn't directly emit greenhouse gases, so it's worth looking into how nuclear could be done better.

It's the same sentiment expressed in Obama's energy plan (though the plan plays down nuclear and gives far more attention to renewables and efficiency): "Nuclear power represents more than 70 percent of our non-carbon generated electricity. It is unlikely that we can meet our aggressive climate goals if we eliminate nuclear power from the table. However, there is no future for expanded nuclear without first addressing four key issues: public right-to-know, security of nuclear fuel and waste, waste storage, and proliferation."

Obama's qualms about nuclear haven't made him unpopular with the industry, though. He's received more than $269,000 in contributions to his congressional and presidential campaigns from executives and employees of Exelon, the Illinois-based nuclear company, NBC reported in February.