Obama speaks at the G-20 summit in Russia. (Sergey Guneev/Host Photo Agency via Getty Images)

President Obama's lengthy news conference Friday from the G-20 summit in Russia came after a long week of senior administration cases for striking Syria, but it was the first time that Obama himself publicly explained his thinking in such depth. He also addressed some of the arguments against his strikes and took a few tough questions about, among other things, mission creep, political opposition and long-term U.S. goals in Syria.

You can read the full transcript here. Below, I've pulled out what looked to me like Obama's big four points, each of which he returned to several times in the lengthy discussion.

1. His goal with strikes is to uphold the norm against chemical weapons – not steer the war

It wasn't a moral case. It wasn't a case for preserving immediate U.S. national security interests. And it wasn't a case about shaping the course of the Syrian war. For Obama, this is first and foremost about preserving the global norm against using chemical weapons – a message that, weirdly, some of his top administration officials seemed to be pushing a bit beyond in their congressional testimony, hinting that strikes could tip the balance against Assad. Here's Obama:

Look, I want to repeat here. My goal is to maintain the international norm on banning chemical weapons. I want that enforcement to be real. I want it to be serious. I want people to understand that gassing innocent people, you know, delivering chemical weapons against children, is not something we do.

2. His long-term goal in Syria is to seek a political solution, not to topple Assad

This is actually pretty similar to point number one. Obama has been saying for months that he doesn't think a "military solution" would be a good idea – in other words, he doesn't want to see the rebels topple Assad and then throw Syria into chaos. He thinks the best, and maybe only, way to end the killing is for the Assad regime to sit down at a negotiating table and craft a peace deal. "We’re not going to get a long-term military solution for the country," he said.

Obama said of his meeting with Russian President Vladimir Putin: "We both agree that the underlying conflict can only be resolved through a political transition. ... it remains important for us to work together to try to urge all parties in the conflict to try to resolve it."

It's easy to warn of mission creep here – and important to watch out for it. When Chuck Todd asked about reports that the Pentagon had been instructed to plan for a wider mission, Obama simply called it "inaccurate." Even if that's true, mission creep is a real risk if the U.S. launches strikes. But it's worth keeping in mind that Obama has always argued that toppling Assad would create more problems than it would solve, that a political solution in which he steps down voluntarily and elements of his regime remain in place is preferable. Whether he could stay that course is obviously a different question.

3. He wants an international coalition but he'll go without one

Obama lamented that "paralysis" in the U.N. Security on Syria means that there's to be no U.N.-approved international response.  "I respect those who are concerned about setting precedents of action outside of a U.N. Security Council resolution," he said.  "I would greatly prefer working through multilateral channels and through the United Nations to get this done." But then he made the case that the U.S. has a special obligation – which also implies it has a special privilege to act unilaterally – when the international community doesn't come together:

There are going to be times, though, where, as is true here, the international community is stuck for a whole variety of political reasons. And if that’s the case, people are going to look to the United States and say, “What are you going to do about it?” And that’s not a responsibility that we always enjoy.

4. Even though strikes are unpopular with Americans, it's still "the right thing to do."

When asked whether he felt chastened by the unpopularity of strikes against Syria, both within Congress and more broadly among Americans, Obama suggested that "people, you know, are struggling with jobs and bills to pay, and they don’t want their sons or daughters put in harm’s way. And these entanglements far away are dangerous and different." But he argued that it could still be the right thing to do, citing the NATO intervention in Kosovo and the failure to intervene in Rwanda. He said Kosovo was unpopular but "the right thing to do," and that a Rwandan intervention "wouldn't poll real well."

Worth noting: Obama suggested that past administrations had sold foreign interventions, for example in Iraq, by using "various hooks to suggest that American interests were directly threatened." Implicit here is that he's declining to argue that Syria poses a direct threat to the United States.