As the row over the so-called "dodgy" Iraq weapons dossier continues, BBC political editor Andrew Marr discussed the significance of the latest developments on the Ten O'Clock News.
The government has been engaged in a very, very important broad argument about why this country went to war against Iraq and, in the end, who you can trust about that.
Over the past few weeks, the whole thing has been diverted into a different argument about the quality of the BBC's journalism.
As a result of today's evidence from government weapons adviser David Kelly, I don't think it's likely that the government is going to be able to prove its case that the BBC's journalism was wrong.
Here is a BBC apology. I said at the beginning of this that in the end heads would roll on one side or the other, one side would be vindicated - government or BBC.
As a result of Dr Kelly's evidence, I don't think that's any longer the case.
We are in the deep, dark woods of question marks all around us and we are not going to be able to pluck truth out of this.
So, one other thing: anybody who has been following this in fine detail probably needs to reconsider their lifestyle.
On a second front, the government has been defeated in the House of Lords over a key part of its legal reforms.
This is really important stuff - trial by jury and indeed the fate of this quite important Criminal Justice Bill.
What we are seeing is an alliance starting to build up on a range of issues - tonight trial by jury, previously foundation hospitals and other issues - between Labour dissidents in the Commons, and Tories and others in the House of Lords.
Now the government will get its legislation through in the end if it is determined. It's got a huge majority and it can force it through.
But it's getting into real problems of exhaustion. It's running out of time and it's exhausting ministers too.
People used to say that this was a government that had a massive majority and could do anything it liked.
I have to say tonight ministers do not seem all powerful and they do not sound all powerful either.