There's an interesting dialogue going on between the New Republic's Alec MacGillis and the New York Times's Ross Douthat on whether any presidency -- much less Barack Obama's in the first year of his second term -- can ever be declared finished.

MacGillis says it's absurd on its face. "First came the government shutdown and the ensuing declamations about the crack-up of the Republican Party," he writes. "Then, with whiplash force, came the obituaries for the Obama presidency. The Washington press corps has been reduced to the state of the tennis-watching kittens in this video, with the generic congressional ballot surveys playing the part of the ball flitting back and forth."

As you can see, this means the Washington press corps is adorable:

Douthat gives the assumption a bit more credence. "What Washington scribes tend to mean when they apply the shorthand term 'finished' to a presidency," he writes, is more akin to what happened to George W. Bush, when "somewhere between the failure of Social Security reform and the 2006 thumping he passed over a crucial threshold where 1) he no longer had a hope in Hades of moving big-ticket legislation through Congress and 2) he no longer had a plausible path to recovering the public’s trust.” The question is whether Obama has hit a similar point of no return.

This is a time when it helps to think less about public opinion and more about the powers of the presidency -- what it can do and what it can't. What matters, in terms of potential accomplishments, is what's left that a president can do. A presidency is finished when it no longer has plausible mechanisms for achievement.

The core mechanism for any president is Congress. Using that mechanism requires willing congressional partners. But since there is little to no chance that Nancy Pelosi will become speaker of House before the end of Obama's term, Obama likely doesn't have a hope in Hades of moving big-ticket legislation through Congress. At this point in Obama's presidency, it's worth being blunt: Barring some game-changing disruption of current trends, Congress is a closed mechanism for Obama.

That has nothing to do with trust in Obama or the rollout of Obamacare. An overwhelming win in the 2012 election wasn't enough for Obama to get a big budget deal with House Republicans. The GOP's fear that it would become demographically irrelevant and Sen. Marco Rubio's endorsement wasn't enough for Obama to get an immigration reform bill past House Republicans. The Aurora and Newtown shootings weren't enough for Obama to get a popular gun-control bill past House Republicans (or even Senate Republicans).

Not done. (Photo by Kevin Lamarque/Reuters)

You can ascribe these failures to whatever culprit you want -- party polarization. Republican extremism, Democratic dogmatism, the White House's weak legislative strategy. The result is the same: Obama was unlikely to pass any more big-ticket legislation long before anyone ever tried to log into That's a huge blow to any administration, and it's a particular blow to this administration, which believed strongly that immigration reform could be the final piece of Obama's legislative legacy.

For that reason, a congressional loss in 2014 won't have the same effect on the Obama administration that the 2006 loss had on the Bush administration. In 2006, Democrats captured both the House and Senate from Republicans, effectively closing off the legislative mechanism to Bush. In 2014, the most Republicans could do is further secure their ability to block Obama from doing anything. Republican gains in Congress would mostly serve to entrench the status quo, not, as was true with Bush, upend it.

The administrative mechanism, however, is much more powerful for Obama than it is for most second-term presidents.

Though Obama isn't going to pass major new laws in his second term, he's going to have plenty of opportunity to implement major laws from his first term. Obamacare's roll-out was disastrous, but the program could be a success by 2017. On Tuesday, the Volcker rule is dropping -- a reminder that the Obama administration is still engaged in a difficult and complex effort to re-regulate the financial system. And then there's the effort to use authority under existing environmental laws to regulate carbon emissions from existing power sources, which could prove a significant climate legacy for a president who hasn't been able to pass a climate bill.

All that's before getting to foreign policy, where Obama also has considerable autonomy. A successful rapprochement with Iran would be a very big deal. So, too, would be destroying Syria's chemical weapons -- particularly if it's somehow coupled with an end to Syria's civil war. And who knows what other opportunities in the foreign policy realm will emerge before 2017?

A second term that defuses Iran's nuclear threat, sets up a successful near-universal health-care system in the United States, re-regulates the financial sector and begins the work of pricing carbon is a pretty consequential second term. Conversely, if any or all of these efforts blow up, the president's second term could become an actual disaster as opposed to simply not very productive.

The Obama administration still has plenty of opportunities to succeed and fail before the end of Obama's second term. But they're primarily non-legislative, and when it comes to domestic policy, they mostly involve successfully implementing the massive laws passed during the president's first two years in office. In that way, Obama's second term is really about making good on the promises of his first.