The Prime Minister dealt with the innuendo about his offshore investments calmly and succinctly in Parliament. His opponents might get a political reward, but only a small one, writes Barrie Cassidy.

It is so often said that politicians - like Caesar's wife - must be above suspicion.

It's certainly true that when life throws up all sorts of hurdles and frustrations, the electorate tends to judge political leaders more harshly than others.

They see and resent so many of the benefits and privileges that exist exclusively for politicians, and for that reason alone, they cut them very little slack when the accusations fly.

In this regard, politicians are often their own worst enemy.

So many of the charges of impropriety or wrongdoing are exaggerated simply because politics polarises. Allegations are inflamed and reinforced in the white hot atmosphere of a parliamentary slanging match. Fair-minded people in the centre might be undisturbed, but the politically committed become agitated to the extreme.

Sorry, this video has expired The politics of envy - has Labor's attack on the PM's wealth worked?

Julia Gillard was put through agony over claims that - because of an association with a dodgy boyfriend in the 1990s - she was somehow involved in the misappropriation of money from a union slush fund.

It was eventually found that Gillard, as a lawyer, had been guilty of a lapse in professional judgment, and nothing more.

Paul Keating in the late 1990s was driven to distraction in the Parliament over allegations about his investment in a piggery on the Darling Downs. None of it amounted to a hill of beans, but it dominated politics for months.

John Howard was at various times accused of everything from genocide against Aboriginal people to war crimes.

Now this week there has been a conjunction of events in Canberra that drew attention to the propriety of both political leaders - Malcolm Turnbull and Bill Shorten.

Labor Senator Sam Dastyari raised the subject of Turnbull's investments through international managed funds, some of which are registered in notorious tax haven the Cayman Islands. The Prime Minister dealt with the innuendo calmly and succinctly in the Parliament, pointing out that all of the taxes on his investments are paid in Australia. He said that if the purpose of Labor's attack is to wear a sandwich board saying he's got a lot of money, go for it!

That won't satisfy everyone. Some of the mud will stick with those who already have a problem with Turnbull's wealth, and who believe that such wealth somehow places him out of touch with ordinary Australians. It will certainly make it more difficult for him to prosecute some arguments around taxation reform and company disclosures.

Politically then, some gain for Labor. But is it fair?

As Senator Dastyari said, "It is all legal and disclosed, but is any of it appropriate?"

OK, ask the same question of Bill Shorten.

Part of the allegations against the Opposition Leader is that companies paid hundreds of thousands of dollars to his union to break demarcation disputes and keep militant unions off sites. Both the employers and the Australian Workers Union got a good result.

That practice was, according to one company executive, commonplace.

So you could argue - as the senator said of Turnbull - it was legal. But again, was it appropriate?

The lesson for both sides might be, leave it alone. Don't ignore the issues. But leave them to those charged with investigating such matters: in the case of Shorten, the Royal Commission, and in Turnbull's case, the Tax Office.

Tony Abbott was relentless in his attacks on Shorten. But in so doing, he diminished himself in the eyes of the electorate, and more to the point, he politicised the commission. He made it all about Shorten, transparently a political exercise.

So far Turnbull has resisted doing that. He is making something of the behaviour of the militant unions, but he is not bringing it all back to Shorten. He knows the commission will do its job. That way he stays above the stench of base politics.

Labor though, by going after Turnbull over the Cayman Islands investments, maintains the tradition of base politics. They might get a political reward, but a small one. The tone of politics has changed since Turnbull succeeded Abbott. Maybe Labor is still playing catch up.

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And just for the historical record, the "Caesar's wife" phrase arose from a particularly sensitive political - and personal - situation.

A Roman of some disrepute - Publius Clodius - disguised himself as a woman to gain entry to Caesar's residence. His purpose - allegedly - was to seduce Caesar's wife, Pompeia. He was charged and acquitted. Caesar said at the time, "My wife ought not even be under suspicion," and the historical idiom evolved from that. Caesar divorced his wife just the same. They were a scrupulous lot back in 62BC. Not only must justice be done, it must appear to be done.

Barrie Cassidy is the presenter of the ABC program Insiders. He writes a weekly column for The Drum.