Tim Russert began last night's presidential debate in exactly the right way: asking all the presidential candidates if they would pledge to have all US troops out of Iraq by the end of the next presidential term: January 2013.

Unstated in the question was that Sen. Hillary Clinton refused to take that pledge this past Sunday.

This presented the opportunity for candidates to distinguish themselves from Clinton, inform primary voters that Clinton cannot be relied upon to end the occupation, and attempt to dislodge her front the frontrunner position.

Last month, John Edwards and Sen. Barack Obama passed up such an opportunity. What about now?

Obama passed it up again. Instead, he echoed Clinton, saying:

I think it's hard to project four years from now, and I think it would be irresponsible. We don't know what contingency will be out there ... I believe that we should have all our troops out by 2013, but I don't want to make promises not knowing what the situation's going to be three or four years out.

Edwards refused to make that pledge as well, but nevertheless, sought to make a distinction with Clinton, and raise questions about her foreign policy objectives:

...I heard Senator Clinton say on Sunday that she wants to continue combat missions in Iraq. To me, that's a continuation of the war...

...when I'm on a stage with the Republican nominee, come the fall of 2008, I'm going to make it clear that I'm for ending the war. And the debate will be between a Democrat who wants to bring a war to an end ... and a Republican that wants to continue the war.

Further, Edwards sought to emphasize that his residual force would be relatively small, between 3,500 and 5,000 troops, in order to protect the US Embassy in Iraq and protect humanitarian workers.

Without taking a pledge to get all troops by Jan. 2013, Edwards' is drawing a very fine distinction, which may limit the political impact.

While some news reports highlighted criticism of Clinton, the AP noted that all three leading Dem candidates wouldn't take that pledge.

Meanwhile, Gov. Bill Richardson and Rep. Dennis Kucinich sought to take advantage of the opening created by the three leading candidates to tout their plans to withdraw all troops from Iraq as soon as possible.

And Sen. Chris Dodd, when asked if he'd take the 2013 pledge to get all troops home, said, "I will get that done."

So you have three candidates -- Dodd, Richardson and Kucinich -- who have pledged to get all troops out by Jan. 2013 (if not sooner). Edwards specifies a low level of residual forces for an indefinite period of time. Clinton, Obama and Sen. Joe Biden were vague about the size of their proposed residual forces.

Clinton also faced criticism, first levied by Mike Gravel, for voting for the Lieberman-Kyl amendment that arguably takes us a step closer towards attacking Iran.

Edwards jumped in forcefully. Noting that both he and Clinton voted for the Iraq war authorization, he said of Clinton's new Iran vote:

We [each] learned a very different lesson from [Iraq.] I have no intention of giving George Bush the authority to take the first step on a road to war with Iran.

And I think that vote today -- which Senator Biden and Senator Dodd voted against, and they were correct to vote against it -- is a clear indication of the approach that all of us would take with the situation in Iran.

Because what I learned in my vote on Iraq was you cannot give this president the authority, and you cannot even give him the first step in that authority, because he cannot be trusted.

So we may have the beginning of an effort to convince voters that Clinton would not represent a substantive change in our foreign policy.

And if primary voters are convinced of that, making Clinton lose her frontrunner status, the whole race opens up again.

Side note: Russert also asked Clinton about Israel's air strike on Syria. Both Russert and Clinton generally accepted the neocon-backed line that Israeli was thwarting a nuclear program in Syria backed by North Korea, and Clinton went as far to say, "What happened in Syria, so far as we know, I support."

While no one knows the full story yet, in my recent LiberalOasis Radio Show interview of Steve Clemons, he cast significant doubt on the nuclear story.