The loss of a senior minister so early on in a government's life would be a serious blow for any new administration - but the loss of David Laws is a particularly wounding setback.
In part this is because Mr Laws was one of the architects of this coalition government.
But, perhaps more importantly, he assuaged the concerns of many Tories about their new Liberal Democrat partners.
Mr Laws was not only a deficit hawk - he at times even seemed to use the same language and arguments as his new Conservative allies.
In short, Mr Laws made Tories comfortable with coalition politics.
He had also proved himself to be a ruthlessly effective chief secretary - carving out a £6bn package of cuts in little over a week.
Nick Clegg - who did not want him to resign - will be painfully aware that he can ill afford to lose such a talented individual to the backbenches.
As for his party, Mr Laws' departure is a warning sign to Liberal Democrat MPs that the stakes in government are an awful lot higher - and the media scrutiny that much more ferocious - than the more tranquil waters of third party politics.