What is Labour's biggest obstacle to getting back into government any time soon? Those who've spent any time thinking about the general election result - and the party still doesn't talk that much about May 2015 - will say that until voters trust the party on the economy, it is not going to succeed. John McDonnell's team clearly agrees, briefing the media today that the reason the Shadow Chancellor is making a major intervention on the economy as he prepares for the Budget is that voters were wary of Labour on the economy.
McDonnell's speech today sounds remarkably similar to the messages Ed Balls offered before the election, that Liz Kendall annoyed members with in the leadership contest and that Rachel Reeves produced in her own speech just days ago. He argues that 'there is nothing left-wing about excessive spending' and pledges exert 'iron discipline' on day-to-day spending, while of course spending more on infrastructure.
Given this is basically the message that Labour offered to voters in 2015, if might take a bit more than this major intervention to convince the electorate. But the bigger problem now is that McDonnell is involved in the leadership of a party that is in chaos, and that appears disorganised. Voters didn't like Ed Miliband as leader and they certainly don't like Jeremy Corbyn. And Labour MPs are far less prepared to extol the virtues of Corbyn or use McDonnell's economic messages than they were with Miliband: many of them actually made rather valiant efforts to conceal their dismay with the leader and his policies.
And until the warfare in the party subsides, it is going to be extremely difficult for even well-crafted messages about the economy to cut through.
So oddly even though McDonnell is right to try to address a serious weakness of his party from the 2015 election, he will find that other serious weaknesses make that much, much more difficult today.