Malcolm Turnbull's message about jobs and growth is becoming increasingly unconvincing as the election campaign wears on, writes Mungo MacCallum.

Malcolm Turnbull's supporters have been praising him for keeping on message, which at least has the virtue of simplicity: my Government has a national economic plan for jobs and growth.

Beauty is truth, truth beauty, and this is all ye know on earth and all ye need to know, as John Keats more elegantly put it.

And certainly our Prime Minister and his dutiful choristers have been hammering the line. But the problem is that it is not only repetitious, it risks becoming boring to the point of irrelevance to many of his potential listeners.

And more ominously, as the message is progressively deciphered, it is becoming increasingly unconvincing. Apart from the various glosses about innovation, trade agreements, youth internships and the rest, the superannuation changes have become seriously divisive within Turnbull's own troops. His own cabinet secretary, Arthur Sinodinos, apparently promised a review after the election and Turnbull himself had to insist that he was staying firm.

But the centrepiece of the whole construction - the plan for short, medium and long term company tax cuts - is proving less and less like a plan for jobs and growth and more and more like a handout to the Liberal faithful. The revelation that the potential - and it is only that - improvement on GNP is a mere 1 per cent over 10 years at the expense of some $50 billion suggests that the result is simply not cost effective.

Turnbull himself has started to hose it down; after all, he says, the initial impact will only be on small businesses in the first three-year term of government, and for the rest - well, that is three elections away. Who knows what might or might not happen then?

In the meantime, we hope that the immediate winners will invest and spend, creating the jobs and growth - well, perhaps just one third of one percentage point of GDP. But even this could be wildly optimistic. Small companies are notoriously conservative: it is only the big end of town that jobs and growth might eventuate, and that is at least a decade away. The smaller players are reluctant even to replace old equipment, let alone to recruit new staff. They are more likely to sit on what they can get, especially in a time when net profits are falling.

So Turnbull has had to admit that the surge he had confidently predicted in budget week will, if it happens at all, be more of a trickle; not much for the first few years and not even a great deal after a decade.

And the same applies to Bill Shorten's recipe for more expenditure on education: there will be an economic dividend, and when it eventually comes it will perhaps be larger and more permanent than Turnbull's prescription, but by definition it will take a whole new intake of pupils to emerge as the success stories.

However, all is not lost: Shorten's proposal to fully fund the Gonski model does provide relief for the schools, parents and children currently disadvantaged. There can be no serious argument that more and better targeted teaching staff will not improve the immediate needs, even if it does not immediately translate into cold, hard economic bottom lines.

Turnbull's rebuttal, that the Government has a plan and that simply more cash is not the answer, is hardly likely to convince those who can see for themselves that in some cases the situation is dire, and that Shorten's idea, no matter how expensive it might seem to the hard-line rationalists, is more worthwhile than a company tax cut. It is, as Shorten keeps reminding them, about priorities.

Which is why, presumably, Turnbull has decided to take out some insurance. Last week he suddenly changed tack: it was not all about the Labor Party, it was also about the Greens, Nick Xenophon, the independents - about just about everyone else, apparently. Only a vote for the Coalition would ensure stability, prevent the alleged chaos of minority government - you know, the system in which Tony Abbott failed to convince the Greens and independents to co-operate in his version of it.

It has finally dawned on Turnbull that in spite of the advice of his machine men that the marginals in the Reps will hold firm, the Senate is still certain to be a melange. The strategy of reforming the voting system has not been the panacea intended; far from weeding out the unwanted recalcitrant, not only will at least a couple of them probably survive, but they are likely to be joined by a few more, and the prospect of the Senate securing a mandate for Turnbull's economic plan is at best problematical.

But it gets worse; if Turnbull loses 10 seats, even calling a joint sitting of both houses to pass the Building and Construction Commission bill may not be an option. His combined majority could easily fall short. And if that happens, the entire exercise - voting reform, bringing forward the budget, the double dissolution, the election itself - will not only collapse, but become a fiasco; many Liberals, not to mention the electorate at large, will ask what the point was.

Why did we have to go through so much pain and suffering only to go back to a hamstrung government with a lot of his backbench followers now thrown into the scrapheap? The horror, the horror.

And of course Scott Morrison is also taking an each-way bet. When the national accounts figures provided an unexpected boost, Turnbull said, "so far, so good" - although he had very little to do with them and his economic plan had not even been formulated during the relevant period. But Morrison warned that things were fragile: the voters should not assume that things were really improving - certainly not rosy enough to risk a return to Labor.

But the implication was that the last two-and-a-half years of the Coalition had still not done anything substantial to repair the economy - F for fail. No wonder the punters are less than convinced about the current prescription.

Mungo MacCallum is a political journalist and commentator.