MPs rejected his Syria policy last week. And now David Cameron faces more unrest over his plans to regulate lobbying.
The 2010 coalition deal committed the Government to new controls on the industry, but little progress has been made, mainly because defining who is and who is not a lobbyist is much like asking the length of a piece of string.
Then, in June, Northern Ireland peer Lord Laird and two of his House of Lords colleagues were accused by The Sunday Times of agreeing to carry out Parliamentary work for payment.
Undercover journalists filmed them appearing to offer to help a non-existent solar energy company. Lord Laird denies any wrongdoing, but the newspaper's claims were seized on by ministers as a catalyst for immediate legislation.
"The public expect us to act," Cabinet Office minister Chloe Smith told the Commons within days of The Sunday Times story.
Quite what the activities of three members of the Lords have to do with regulation of Westminster's £2bn lobbying industry was unclear, but the Government pressed on.
The Bill it produced, as well as failing to define commercial lobbyists properly, also unfairly targets the charity sector.
The legislation will apply in Northern Ireland. Although it does not seek to regulate the Assembly's links with lobbyists, it will affect how groups here can campaign in the year before a Westminster election.
For example, a local homeless charity decides to run a campaign advocating more public spending on housing some time between May 2014 and the General Election. If one political party wants to increase spending and others do not, the charity could have to register as a recognised third party with the Electoral Commission.
If the campaign is deemed to have an effect on an election, even if that was not its purpose, the charity would have to declare its campaign spending, including staff costs, as "election spending".
The burden of bureaucracy on a small charity and possible criminal sanctions, it is predicted, will have a chilling effect, closing down debate on matters of public concern.
The Government says charities have nothing to fear, as they will not be covered by the legislation.
But the Electoral Commission disagrees, warning that it could apply to "many of the activities of charities that engage in debate on public policy".
A Belfast-based lobbying company is not covered by the legislation if it lobbies the First Minister or Executive civil servants, but if it lobbies the Secretary of State, or the Northern Ireland Office's permanent secretary, it will have to register.
Many a bad law has been made in haste and the Transparency of Lobbying, Non-party Campaigning and Trade Union Administration Bill is on course to become a textbook example.