By James Coomarasamy
BBC News, Washington
In the initial stages of an unusually early and crowded US presidential race, one issue has been crowding out the others: the war in Iraq.
It is especially true on the Democratic side, where the three candidates currently leading in the opinion polls are all calling for an end to the American presence in the country, but in very different ways.
Hillary Clinton and John Edwards both cast votes in the US Senate in 2002, authorising President Bush to invade Iraq.
Senator Clinton has honed her security credentials over the years
John Edwards, the former vice-presidential candidate, now says - openly and frequently - that he made a mistake.
Hillary Clinton - who has carefully nurtured her national security credentials during her six years in the Senate - takes a different view.
If she'd known then what she knows now about weapons of mass destruction, she says, she would have acted differently.
But, she says, if the same evidence were presented to her now, she would do the same again.
According to her, that 2002 vote wasn't a mistake. She doesn't regret it.
What she does regret is how President Bush used the authority that she - and others - gave him.
That is a nuanced position, which the wider American public may see as a principled one, and as evidence of the consistency and strength needed in a commander-in-chief.
The problem is that it's not the public at large, but the anti-war grass roots of the Democratic Party who will determine their nominee.
According to Norman Ornstein of the conservative American Enterprise Institute: "The Democratic party's liberal, activist base is emotionally completely caught up in its visceral reaction to this disastrous war."
In that context, Senator Clinton's position is a gamble.
The leading Democratic candidate with the purest anti-war credentials would appear to be Illinois Senator Barack Obama.
He doesn't miss an opportunity to remind audiences that he was against the invasion in 2002, when he was serving not in Washington, but in the Illinois State Senate.
Yet he, too, has already stepped into the political minefield which Iraq presents.
He was forced to apologise after talking about "wasted" American lives during a speech he made in New Hampshire.
That's a trap into which even the most experienced politician can fall, as Republican presidential candidate Senator John McCain discovered, when he announced on the late night David Letterman Show - to a universal lack of surprise - that he was running for president.
A hero of the Vietnam War who has called for more, not fewer troops in Iraq, he, too was criticised for when he referred - in his announcement - to "wasted American lives".
Senator McCain apologised for talking about lives "wasted"
But - for the moment - Iraq is less of a factor in the race for the Republican nomination.
The candidate currently leading in the polls, the former New York mayor Rudy Giuliani, has broadly supported President Bush's policy.
So, too, has another early favourite, Mitt Romney, the former governor of Massachusetts.
Only Sam Brownback, the conservative senator from Kansas, has gone out on a limb and questioned the decision to send more troops into the country - not that his stance has done much for his poll numbers, which remain in the single digits.
Loyalty to Bush
For, while President Bush's ratings may be down, he still remains popular within the Republican ranks.
Mr Ornstein of the American Enterprise Institute says: "At this point, to get distance from the president on Iraq would not only look disloyal, but it would grate with enough of the Republican activists that it would damage a candidate."
So - for the time being - it is the position of the Democratic candidates that is being the most closely scrutinised.
The primaries are still many months away, but with so much at stake in Iraq, every vote that they cast and every speech that they make on the issue could prove decisive to their presidential chances.