Eaton, a former infantry officer, had a 30-year Army career that including deployments to Somalia, Bosnia and Iraq. After retiring from the Army in 2006, he criticized Rumsfeld that March in a widely read op-ed for failing to understand counterinsurgency and, indeed, the nature of the Iraq war more broadly. Later he signed on with Hillary Rodham Clinton’s presidential campaign before supporting Barack Obama in the general election.

At NSN, Eaton’s official title will be a senior adviser, but he’ll be the public face of an organization set up after the Democratic defeats of 2004 to bridge the policy and messaging divides between the progressive and national-security communities. NSN employees describe him as a “bonding agent” between progressive politicians and the military: while NSN has had no shortage of national-security experts on its roster, Eaton is the first retired flag officer to sign up. With progressives divided over what to make of the Afghanistan war, Eaton’s new role should be one to watch, as NSN has taken a cautious position in favor of the administration’s strategy. He starts on Monday.

NSN’s original leadership has been absorbed into the Obama administration. Founder Rand Beers, the former White House counterterrorism chief, is now an undersecretary at the Department of Homeland Security, where original communications director Moira Whelan serves as deputy in the Office of Gulf Coast Rebuilding. Ilan Goldenberg now has a large part of the Iran and Israel portfolios in the Department of Defense’s policy directorate.

(Full disclosure: I’ll be taking part in a National Security Network-sponsored panel discussion on Afghanistan at this year’s Netroots Nation conference in Pittsburgh next month.)

It’s safe to say that Goldenberg, 31, has his own take, though he declined comment for this post. His writings for the past several years on the liberal security-matters blog Democracy Arsenal indicate that he’ll press both the Israelis and the Palestinians to honor their commitments toward reaching a two-state solution, and he’ll seek creative outreaches to Iran. Here, for instance, Goldenberg endorses a U.S. push for an Israeli-Syrian peace accord as “the type of game-changer that improves America’s image in the region, generates positive Israeli political momentum towards [peace], weakens Iran, Hamas and Hezbollah and in the long-term could potentially improve the likelihood of an Israeli-Palestinian agreement.” Here‘s Goldenberg pushing back on the idea that American Jews uniformly backed Israel’s Gaza war. Here‘s Goldenberg praising the appointment of “serious heavyweight” peacemaker George Mitchell as the administration’s Arab-Israeli special envoy. And here‘s Goldenberg advocating early and urgent engagement with Iran, before the forthcoming Iranian presidential elections, since “there is nothing that makes Iranians more suspicious than the idea that the U.S. has a vested interest in the outcome of their elections.”

What’s more, Goldenberg — full disclosure: a friend — made this interesting observation about emerging trends in progressive national security thinking last November:

[W]hat you now see forming is a broad consensus among liberals, liberal hawks and realists.  There is relatively universal agreement among these groups that we need to begin withdrawing from Iraq, focus more on Afghanistan, opt for direct diplomacy with Iran, reengage with the world, improve our image, strengthen our alliances, close Guantanamo and deal with global warming and energy security.

That is a pretty broad consensus and it’s one that politically was first pushed hardest by the left.  On the traditional right-left spectrum, you would have to call this a solidly left of center consensus that  has in fact been Obama’s foreign policy platform for the last two years.

Goldenberg might have mentioned that his efforts as part of NSN were a large part of pushing that consensus leftward. Before NSN, there wasn’t a progressive organization that could call together policy wonks and politicians to work out both messaging and substantive, principled policy thinking. It’s no coincidence that two of its other early heavy-hitters, former White House counterterrorism chief Rand Beers and ex-Hill staffer Moira Whelan, are now at the Department of Homeland Security. (Beers is awaiting confirmation as an undersecretary; Whelan is communications director.) Goldenberg isn’t the most senior person on the Obama Middle East team by a long shot. But the difference between where the Democratic Party was in 2004 on national security and where it is today — both substantively and stylistically — testifies, in part, to his ability to have real impact.

Goldenberg is scheduled to start at the Pentagon next week. His last day at NSN is said to be Friday.