When religious leaders across the spectrum line up to say your policies have created a "national crisis" of hunger and poverty, when your government is forced to push out a long-delayed report that comprehensively debunks your already obviously weak explanation for the explosive growth of food banks, it really isn't a great idea to claim that your policies were driven by a "moral mission".
The biggest blow delivered to Cameron over the course of the past week came from an unexpected source.
Last Wednesday, I joined protesters outside Atos's office in London speaking out about the dreadful Work Capability Assessment (WCA) and the obscene profits the company makes from it.
Strikingly, Atos is now looking better than the government after it emerged that the company, sick of being a byword for inhumanity and ineptitude for administering the WCA, has asked to be excused from the contract.
That doesn't exonerate it for the years of misery, fear and suffering it has inflicted on the people of Britain unfortunate enough to have a disability or suffer from illness. The finding of the Public Accounts Committee last year that Atos was making huge profits from a test while the government bore the cost of the huge number of appeals against its findings, 38% of which have been successful, means they still have huge culpability. If Atos wants to make reparations, it should donate all of the profits it has made from the tests to disability charities.
But Mr Cameron has made much-hated Atos look good by comparison - really a new low in his stint as PM, which is already defined by a failed policy of austerity and its resulting widespread poverty, Victorian levels of inequality, and missed opportunities to restructure our economy.
So my advice to the Prime Minister? Now's the time to see the light - to accept the findings of the judicial review that concluded is the Workplace Capability Assessment isn't fit for purpose. You could blame the former Labour administration for introducing the flawed system, and then you could introduce an alternative that trusts the people best placed to judge whether an individual is or isn't fit to work - the medical professionals who are treating them.
It's also time to admit that the Personal Independent Payment (PIP), set up to replace Disability Living Allowance (and slash payments), is also punishing people simply for having a disability, and will be an equally huge black mark on your record if you don't act fast.
For WCA and PIP, swapping one outsourcing giant for another is no kind of answer - and it's hard to imagine any company would welcome the kind of opprobrium Atos will carry for many years.
On food banks, the problem is more complicated.
Certainly, Mr Cameron, a good start would be to agree with your chancellor, George Osborne, and push the minimum wage up significantly. The Green Party has long been calling for it to be set at the level of a living wage, and that would provide additional income for the Treasury.
When Green MEP Keith Taylor and I recently visited Winchester food bank, volunteers there were noting how more and more of their users were young working families.
You must also recognise and acknowledge that unreasonable sanctions put on benefit recipients, and failures of administration in benefits are a huge part of the reason that hundreds of thousands of people are forced to use foodbanks in Austerity Britain.
Acting on even one of these proposals, Mr Cameron, might just result in a better week for you. Perhaps you could even use the word "moral" without it flying back in your face.
At least the very least, you should be able to sleep more soundly in your bed, knowing that you've saved some Britons from government-inflicted hunger, fear and misery.
Follow Natalie Bennett on Twitter: www.twitter.com/@natalieben