Media sentiment is akin to market sentiment in the City. Journalists move as a herd, are nervous about going against public opinion and generally seek the comfort of the crowd. The lobby system, where political correspondents are all located in Westminster, reinforces the trend. If a story gathers momentum on a particular trajectory, it is difficult to stop. Every new fact or comment is twisted to fit the prevailing story. When sentiment is heading your way, you can't go wrong and everything you do is portrayed as a success. When sentiment is against you, everything you say is doomed to backfire.
The prevailing story since the last election has been 'cuts'. Last weekend, David Cameron made another attempt at moving the story on by dedicating his spring conference speech to enterprise and job creation. The speech built on an earlier attempt in the New Year to highlight the positive steps being taken to rebalance our economy and create private sector jobs.
It is always difficult to judge when 'the story' is ready to change. It is based, in part, on the degree of media fatigue with a particular line of reporting and in part on the power of big events to create momentum in a new direction. Cameron understands the latter more than most. He used the party conference in 2005 to win the Conservative leadership and the conference of 2007 to vanquish Gordon Brown.
All politicians can do is use key events when the mood is fluid to change sentiment. The Libyan crisis means that the spring conference could never be a game changer, but it did set the scene for the next big event, the Budget. Meanwhile, Ed Miliband has squandered his honeymoon. When the media narrative does reverse, he's in trouble.