Given the opportunity in Sunday's ABC debate to distinguish themselves from Sen. Hillary Clinton on Iraq, Sen. Barack Obama and former Sen. John Edwards passed.
Which raises the question: how do they think they are going to dislodge her from her front-runner position?
Yes, it's early, and lots of things can happen. Polls five months out are notoriously poor indicators.
But Clinton is as vetted as a candidate can be. It's hard to see a surprise scandal, and she's not making many self-inflicted wounds.
If something is going to happen, in all likelihood, a rival candidate needs to make it happen.
He will need to a make a compelling case why Clinton should not be the nominee. It's not at all clear that there is a large enough "Anybody But Hillary" contingent for a single rival to try to consolidate.
Presumably, Iraq would give a rival such an opening.
Not only does she have a weak history on the subject -- with her unsatisfying explanations of her war authorization vote.
But she is the only candidate who reportedly believes that we should have US troops in Iraq by Jan. 2017 at least.
She has not said that publicly, but Ted Koppel has reported that she privately told a former Pentagon official who has briefed her that "she would still expect U.S. troops to be in Iraq at the end of her second term."
All of the candidates (including Clinton) have said they reject the neocon goal of permanent military bases in Iraq.
And Edwards and Obama share Clinton's view that after the withdrawal of combat troops, a residual force should stay behind temporarily but indefinitely.
However, a residual force that isn't gone by 2017 (if not sooner) doesn't look very temporary, making the combat troop withdrawal worthless as far as changing Iraq's political dynamic.
To date, Edwards has tried overtake Clinton by arguing that Clinton is too close to lobbyists and corporations, and doesn't have specific enough policy proposals.
But most Dem primary voters, generally pleased with her husband's presidency, do not seem mistrustful of what she would do in the domestic policy arena for such charges to stick.
Obama has quibbled with her over foreign policy tactics, questioned her judgment in voting for the Iraq war authorization, and alluded that she could not bring the country together as well as he could.
None of that has proven significant enough to primary voters for them to justify throwing a front-runner overboard.
But perhaps, if voters believed Clinton would not really end the war -- and primary voters really want to end the war -- that would gives voters pause.
Yet when Sunday's debate moderator George Stephanopoulos prodded the candidates to clarify their differences on Iraq, neither Edwards or Obama exploited the opening.
Edwards argued that their differences on Iraq were very minor:
I know you're trying to create a fight up here, I understand that, but any Democratic president will end this war...
... the differences between us -- whether it's Senator Clinton or Senator Dodd or Governor Richardson or Senator Biden, all of whom I have enormous respect for -- the differences between all of us are very small compared to the differences between us and the Republican candidates, who the best I can tell are George Bush on steroids.
And when asked, "Is there any difference between you and Senator Clinton on what you would do right now," Obama dodged the question:
My sense is that what all of us need to do over the next 16, 18 months is focus on putting pressure on Republicans to stop giving George Bush a blank check. Because if we have to wait for 16, 18 months, that's going to make the situation that much worse.
If we have not began a withdrawal by the time I'm sworn into office, then the next task is to call together the Joint Chief of Staff and to give them the mission -- which is to begin an orderly, phased withdrawal, so that we can begin the diplomacy that Joe [Biden] and Bill [Richardson] and others are talking about.
Of candidates registering double-digit poll numbers, only Gov. Richardson is making future Iraq policy a point of difference, criticizing the "top-tier" candidates for supporting a residual force, instead of a complete withdrawal.
Arguably, that's the reason why Richardson is the only "second-tier" candidate to move out of single-digit territory (but because of stumbles and uninspiring positions on other issues, he hasn't been able to build on that momentum.)
Edwards and Obama appear to have shut the door on distinguishing themselves from Clinton on this critical point.
That is their prerogative.
But they should recognize that if voters are not currently unnerved by the prospect of a Clinton nomination, they will need to make bigger distinctions that speak to major concerns of voters, if they are to derail a coronation.