Chris Mason: Dissent fizzes again at the top of the Labour Party

After the spray of resignations, fury and anger a month ago following Labour's calamitous election results, the Makerfield by-election campaign had put a temporary cork in the bottle of the party's dissent.

It turns out we didn't have to wait to find out if the Greater Manchester Mayor Andy Burnham would be returning to Westminster before the bubbles of anxiety about Sir Keir Starmer would be visible again.

The prime minister had sought to seize this brief opportunity to project direction and delivery and saw the Defence Investment Plan, or DIP, as a case study in both.

Instead it has become the latest example - according to his departing ministerial critics - of his inability to get things done.

He has his work cut out now to stop that becoming the epitaph to his premiership.

The DIP, alongside the anticipated imminent announcement about a crackdown on social media access for teenagers, was meant to be one of the weighty announcements that Sir Keir could point to and so draw a contrast between what he was doing in government and what his ambitious wannabe successors were doing at the same time – plotting and schmoozing with Labour MPs.

But now, days before he heads to the G7 summit of world leaders in the south of France, he faces a fresh setback.

Defence Secretary John Healey resigned on Thursday, writing in his letter to Sir Keir that the level of military spending proposed by the prime minister "falls well short" of what's needed to protect the country.

Sir Keir's new Defence Secretary Dan Jarvis, a veteran of tours of duty as a soldier in Northern Ireland, Kosovo, Iraq and Afghanistan, is due at a Nato defence ministers meeting next week where he will have to explain this embarrassment to his peers.

Jarvis and Sir Keir are also on the lookout for a new armed forces minister, after the bizarre resignation of Al Carns.

Carns, another former soldier, did a couple of television interviews on Thursday night, including one with me, while still a minister, in which he said "my job is to steady the ship".

An hour later, he jumped off the ship and resigned.

Surveying all of this are Sir Keir's potential leadership challengers Burnham, Streeting and others – including Carns, who told me, while still a serving minister, that as far as a leadership contest was concerned, "if someone fires a starting gun, I'm not scared of gunfire".

And surveying it too are Downing Street and the Treasury, who are bruised and winded after another one of those days.

They maintain they were doggedly striving to find a deal on defence that they could sell to the armed forces and to defence ministers, sell to the rest of the government and ultimately sell to the country.

On the first of these they failed, on the second they were struggling and courtesy of both of those things they have not yet had a chance to try to sell it to the rest of us.

The prime minister's allies maintain that he is patiently wrestling with the most difficult of backdrops and so a series of fiendish trade offs: a sluggish economy, a high overall tax burden, growing benefits bills, a dangerous world and so demands for huge additional defence spending.

Other government departments had already been told cuts were coming for them to switch money to defence.

The Conservatives and others say welfare must be slashed to help the armed forces.

Sir Keir now has to try, yet again, to pick himself up and go out and make the case for his flailing premiership.

He must know his chances to do so appear to be shrivelling yet further.