On the surface, there is a gaping divide between, and within, the parties over the Government's plans to extend the 28-day limit for detaining suspects without charge. At the moment, no other topic raises passions in quite the same way.
In the past, it has suited leaders to play up the differences for a variety of reasons. Gordon Brown cannot think of a policy without erecting a dividing line with the Conservatives. "Tough on security versus weak" must have seemed a pretty good one in the summer.
For their part, the Conservatives probably lost some of their interest in consensus when they sensed two years ago that Tony Blair could be defeated over the issue, a defeat in which Blair lost much of his prime ministerial authority. Political calculations always play their part.
But the potent mix of expedient posturing and principled conviction obscure the potential for common ground. In his statement to the Commons yesterday, the Prime Minister moved tentatively on to this unexplored terrain. In relation to the 28-day limit, he made only a single point during a long speech. Brown expressed a hope that consensus could be found over the circumstances in which an extension might be necessary.
That consensus already exists. The Conservatives accept there might be exceptional occasions when the police need more time. The overseer of security legislation, Lord Carlile, argues also that such circumstances might arise. As a Liberal Democrat, he does not speak lightly on such matters.
So, at the very least, Mr Brown makes a tonal shift. He could have crusaded wildly about the need for a 56-day limit and argued that the Tories were being weak in opposing such a move. He could also have made it the centre point of the speech. Instead, he chose to highlight fleetingly the area on which there is already a degree of agreement between the main parties in relation to this issue.
There was no overt game playing. Indeed, Mr Brown's overlong statement in the Commons yesterday was so undemonstrative that he lost the attention of MPs from both sides as he delivered his words. In the post-Blair era, Brown eschews theatricality, but in doing so he can go too far. If he does not watch it, he will lose the attention of the bigger audience outside the Commons.
Nonetheless, Mr Brown is nearly always astute, even when he is being dull. If he establishes a consensus that an extension might be needed in unusual circumstances, the debate moves on to how the extension could come about.
Even on this next phase of the debate, the divide is not as big as it seems. The Conservatives argue that legislation already exists in an emergency to detain suspects for another 30 days. Therefore, in theory, they accept that in extreme circumstances suspects could be held for 58 days.
Brown's proposals differ, but not greatly so. He argues that if the police want more time they should be able to apply for a seven-day extension, a move that must be granted by the Director of Public Prosecutions and a High Court judge. The extension must be renewed every seven days, and renewal must be permitted only up to a limit. Obviously, there is disagreement as to what that limit should be, but Downing Street stresses that 56 days is an "upper limit".
The bulk of Brown's balanced statement yesterday was on practical security measures and some important initiatives aimed at winning the so-called "hearts and mind" debate. David Cameron welcomed most of them. As he pointed out, his party had suggested some of the proposals in the first place.
I do not seek to play down the potential for provocative authoritarian clumsiness. We have no better witness as to the dangers than the security minister, Lord West, who told yesterday's Today programme that he would need to see the evidence for such an extension to be granted. Lord West agonised aloud on the BBC about the balance between security and civil liberties. He was at liberty to speak his own mind for around an hour. After his subsequent meeting with Brown, Lord West declared that he supported an extension from 28 days.
Last week the Home Secretary, Jacqui Smith, admitted on Today she was not sure how long the extensions should apply. She did not even try to crusade over the issue or score political points.
Lord West's comments on Today were both illuminating and a red herring. As a new Prime Minister with an unfair reputation for Labour tribalism, Mr Brown created a big tent in the summer by inviting outsiders to his government. In a pre-election context, the symbolism was potent. Now there is no election he is stuck with politically naïve ministers for at least another 18 months. The highly political act of setting up a big tent makes him dependent on those who are not political.
Politics is partly an art form that can be mastered only over time. Like learning a language or a musical instrument, there are many considerations to take into account. The ministerial outsiders such as Lord West are being asked to play lead guitar at Wembley without having had a single lesson. However competent, they will make mistakes in the art of politics. Lord West was candid on Today and spoke against the policy he will be partly responsible for implementing.
And yet, even in the case of Lord West, the gap between his own views and the Government's policy is not gaping. He wants to see the evidence before an extension applies. Presumably the DPP, a High Court judge and Parliament would want to see the evidence as well. These are the safeguards that would apply under Brown's plans.
Two years ago Tony Blair proclaimed that it was better to be right and lose over his determination to get an extension to 90 days. Now we have the security minister admitting that evidence is required, and a Home Secretary accepting that she did not have a precise limit in mind. Yesterday we had a new Prime Minister highlighting the area in which there is some consensus between the parties. The political mood feels different to two years ago.
Perhaps there will still be a titanic clash between Brown and Cameron, Jacqui Smith and David Davis. Perhaps Brown will lose, Blair-like, in the Commons after another authority-draining backbench revolt. But I sense it will not end like that and there will be a way through the differences within the Government and between the parties.
I am not predicting that, as a result, the correct balance will be achieved between civil liberties and security. For now I predict only that, in terms of the political dynamics, we are moving on to a phase in which the parties realise it is in their interests to reach agreement rather than exaggerate the divide. When leaders have claimed they would like to reach consensus, they have not always meant it. Now they do.