This story will probably rule the news cycle this weekend. The light-water reactor at Bushehr in southwestern Iran is to be fueled starting on August 21 and powered up in September. I’ve written about Bushehr’s significance several times (here and, earlier this week, here). The Bushehr reactor doesn’t have the meaning to Iran’s nuclear weapons program that the Iraqi and Syrian reactors had. Although the reactor could figure in Iran’s weapons program in the future, it’s not central to the production of weapons-grade material. I very much doubt Israel regards it as necessary to strike the Bushehr installation.

But fueling the reactor and powering it up send the clearest possible political signal: that Russia and Iran feel free to do it. The uranium fuel — provided by Moscow — has been stored in Iran since 2008, but Russia has held off on preparing the reactor for operation, largely because of calculations about U.S. objections. Timing the reactor start-up to squeeze more concessions from Iran was probably a factor too.

I suggested a few days ago (see the link above) that the coordinated rocket attacks on Israel and the attack by Lebanese troops on an IDF contingent in the north, which occurred on August 1 and 2, were related to the plan for Bushehr. Iran has been skittish all summer, fearing an imminent attack; powering up the Bushehr reactor is an event the mullahs probably expected to want some insurance for, in the form of a preoccupied Israel.

But whatever qualms the Iranians or Russians may have had about taking this action — one that directly contradicts the intent of UN sanctions and U.S.-EU policy — they appear to feel them no longer. The real significance of starting up the reactor next week is that Iran and Russia don’t fear doing it.

I predict we will hear from the Obama administration that this action is unhelpful, but that in a technical sense, it’s not all that important. And in a technical sense, it’s not. But in a political sense, as a signal of how seriously Iran and Russia take U.S. policy, it means everything that matters.