In a sure sign the Coalition government is worried about voters being attracted to Labor’s campaign on inequality, the prime minister renewed efforts this week to paint Bill Shorten as a dodgy imitation of inequality heroes like the UK’s Labour leader Jeremy Corbyn.

Mr Shorten has closely watched the progress of his counterparts overseas and learned that envy trumps optimism. Mr Corbyn in the UK and Bernie Sanders in the US have demonstrated that resentment and anger over inequality are more powerful in attracting votes than optimism and the free-market thinking that attracted aspirational voters to John Howard and Kevin Rudd.

Mr Turnbull can’t change that equation. It’s too powerful when a whole generation has been priced out of the Australian housing market, but he believes he can limit Labor’s ability to exploit it by painting Mr Shorten as a false prophet.

That’s why you’ll be hearing more about the Opposition leader’s union days, in the days and weeks to come.

This week, the government worked with the not-so obstructionist Senate crossbench (except Jacqui Lambie, who voted with Labor and the Greens) to pass a law that makes it a criminal offence for secret payments to be made between employers and unions.

Payments, it just so happens, like the one that Bill Shorten only just remembered to declare prior to his appearance before the royal commission into union corruption.

Just in case we missed that point, Mr Turnbull declared during a press conference on the matter that, yes, Mr Shorten’s conduct would have attracted “criminal sanctions” if the law had existed when he accepted the “secret” donation as a union leader many years ago.

Other banned behaviour would be “a union official who gets onto an employer’s private jet, enjoys a holiday in Cuba while sipping Cristal champagne but at the same time is negotiating an agreement with the employer.”

Mr Shorten had also done that, according to the PM.

“Labor has stood up for secrecy and corruption. We have opposed it,” Mr Turnbull told the assembled journos.

The PM is playing with fire, however, by trying to paint Labor as the only party of bagmen and crooks. Voters haven’t forgotten the Liberal MPs and officials whose secret deals and payments were uncovered by the NSW ICAC.

Then there’s Victorian state Liberal leader Matthew Guy who apparently has some explaining to do about the political donation he claims to have not discussed when he attended an expensive dinner in April with an alleged underworld figure.

In fact, any allegations levelled by one major party against another on secret payments and “forgotten” donations simply fall on deaf ears. Voters dismiss the jibes as another example of the pot failing to look in the mirror before making accusations against the kettle.

Having said that, it was nevertheless galling to see one of the past masters of dodgy political behaviour crow about his expertise in the media this week.

Using the opportunity to cast even more doubt on Matthew Guy’s account of that infamous dinner, former Labor minister and party bagman, Graham Richardson, recounted in his weekly column that as a party official he would collect donations from “those whom you would not take home to meet the family”. This was to ensure that, “if anyone had to be thrown under the bus,” presumably due to the questionable nature of the donations, “it would be me.”

Mr Richardson noted one occasion when he collected a “large cheque” from a “poker machine magnate” and another when it appears he duped the late Don Dunstan, Labor premier of South Australia, to receive a “very large cheque” from an alleged owner of an illegal casino.

According to Richo, “no laws were broken because electoral funds checks and balances hardly existed in those times.”

Yes, that’s an unedifying display of hubris, but it would be a mistake to think the political culture that produced Graham Richardson in the Labor Party did not create his equivalent in the Liberals. The corrupting nature of political donations is all-pervading, and in urgent need of reform.

That’s why Malcolm Turnbull’s strategy to undermine Bill Shorten’s credibility is an ill-advised one. Each time the PM points the finger at his opponent, voters will simply think “your lot are just as bad.”

Paula Matthewson was media adviser to John Howard in the early 1990s and then worked for almost 25 years in communication, political and industry advocacy roles. Paula tweets at @Drag0nista.