By Mark Mardell
BBC News political correspondent
"There's no point denying it, Tony has taken a serious hit over Iraq," one of the prime minister's strongest supporters in Cabinet sighed as he leant back on his ministerial sofa.
The decision to go to war in Iraq was contentious
He continued. "But while Iraq means Iraq to some people, to others it means something else."
This rather Delphic utterance just goes to underline what an indigestible event the Iraq war was for this Labour Government and for the prime minister.
This should not be a surprise.
Mr Blair's decision was without precedent: no other leader in a democracy has ever taken a country to war, when it was not immediately and directly threatened, with the voters' support for the action hovering around 50%.
It would have been contentious in any case, but the failure to find weapons of mass destruction undermined the stated case for war and even produced a half-apology from the Prime Minister.
IS IT DEVOLVED?
Scotland: Not Devolved
Wales: Not Devolved
NI: Not Devolved
Devolved issues are the responsibility of the Scottish Parliament, Welsh Assembly, or NI Assembly
Iraq is the background to this election. That doesn't mean it will be an issue.
While some interviewers will question the prime pinister on the detail of his decisions, and some voters may be interrogating him about his position, it is unlikely to intrude into the central debate between Labour and the Conservatives.
But it may help dictate the tenor of the campaign, and even its result.
Robin Cook was the first minister to resign over Iraq
Many Labour party members felt uncomfortable about the war. Some resigned over it.
It undermined trust in Tony Blair, and trust in his judgement.
It shoved in their face his belief in America's role as the only superpower, and his zeal for military interventionism.
Some ministers are worried that this demoralisation will have an effect on their fighting strength on the ground during an election.
They have already noticed that fewer people are willing to come out and leaflet or knock on doors.
Many local parties simply aren't in a terrific state to fight an election.
MPs in seats with large Muslim populations are nervous: they have already lost two by-elections to Liberal Democrats when this was clearly a factor.
Lib Dem hopes
And what about those Liberal Democrats?
The party opposed the war (as did the SNP in Scotland and Plaid Cymru in Wales), striking a chord with many Labour supporters.
The Lib Dems hope some Labour voters will switch to them.
Even if they don't, the Government is nervous about the effect on Lib Dem supporters who made a tactical decision in the last two elections to vote Labour.
Are they not now more likely to return to their real home?
Those are the voters for whom, in the words of that cabinet minister, "Iraq is about Iraq."
He and the Labour Party are probably more worried about the others, for whom Iraq means something else.
These are often traditional working class labour voters who weren't particularly bothered about the war itself.
But some have a perception that Mr Blair is more concerned with abstract issues of foreign policy than dealing with the day-to-day domestic grind that affects them.
Once natural supporters of a party start thinking that its leader is not really bothered about them, then that is potentially serious.
The Tories have accused Mr Blair of lying over WMDs
Conservatives are also hoping to exploit the feeling among the electorate that Mr Blair is untrustworthy because of the war.
They have accused the prime minister of lying over weapons of mass destruction.
And they have accused the Labour Party of playing fast and loose with civil liberties in introducing a prevention of terrorism bill that would allow the home secretary to detain suspects in house arrest without a court order.
But the Tories want to play it tough, too.
They support regime change in Iraq and have accused the government of making dangerous cuts in defence spending.
Tough on defence
But they may have an uphill struggle.
Labour struggled for years with a perception that it was soft on defence, not willing to fight to protect Britain.
Few think that now.
They may not be vocal, but there are many voters who are impressed by Tony Blair's resolution and determination.
Ministers are beginning to construct a case that Iraq was the first domino that will lead to the fall of dictatorships all over the Middle East.
But Mr Blair won't win many votes on the issue that has defined his second term as Prime Minister.