<i>Illustration: Rocco Fazzari</i>

Illustration: Rocco Fazzari

Tony Abbott thought about offering one of his senators a diplomatic posting. Not so much because he thought it would be a good appointment but because he wanted him out of the way.

You probably have not heard of Senator Ian Macdonald. He is not the corrupt former NSW Labor politician who conspired with Eddie Obeid- that is another Ian Macdonald, no relation.

The Abbott government's Ian Macdonald isn't really noted for any particular reason, even though he'll have been in parliament for 24 years on July 1. Even though he was a minister in John Howard's government, twice.

Howard dropped him from his ministry to make way for younger and more thrusting politicians. And although Macdonald was a shadow parliamentary secretary in Tony Abbott's opposition and could have expected to be appointed a minister in his government, Abbott disappointed him too.

"What should have been one of the proudest days of my life has turned into one of the worst," said the 68-year-old, who prides himself on being a champion of northern Australia.

"The ecstasy of a new government and success in the north has turned a little sad with a phone call from Tony Abbott saying he has no room for me in the new ministry."

Abbott weighed the idea of offering him one of the lesser diplomatic prizes as a consolation. In the event, he didn't. Because he remembered what happened when Howard had offered him consul-general in Los Angeles.

Macdonald's response had been to tell his prime minister to "shove it up his arse," in the words Macdonald has used to his colleagues. He rejoiced in his status as a man with nothing to lose and became a leading internal critic of Howard's prime ministership.

So Abbott decided not to give Macdonald the satisfaction of turning him down. "He just wants to poke the PM in the eye," as one member of the Abbott team put it. "He's a fairly belligerent character."

Macdonald is finding other ways to poke Abbott in the eye.

He won headlines in December for rising in the Senate to denounce the Abbott office in an attack that was clearly aimed at the prime minister's chief of staff, Peta Credlin. The office seemed, he said, "to have an almost obsessive centralised control phobia."

He won't be promoted, he can't be bought off and he won't shut up. Ian Macdonald, in other words, is trouble for Tony Abbott in the Senate. His vote cannot be relied upon. He has just been elected to another six years. And he is a member of the Liberal National Party, supposedly one of Abbott's own team.

In the weeks ahead, with the West Australian senate election to be re-run on April 5, there is going to be plenty of commentary on the Senate.

The big question will be: Can the Coalition keep its three WA senators elected in September, or will it lose one as support for the government ebbs?

Either way, the Abbott government will not have a majority in the Senate. Either way, it will need to wrangle votes from the eight independents and minor parties that will fill the crossbenches in the 76-seat chamber.

The balance of power in the upper house of parliament will be in the hands of these eight, a collection of political novelties and chancers that Channel Seven's Mark Riley has described as being reminiscent of the bar scene from Star Wars.

These will likely include a senator from the Motoring Enthusiast Party, another from Family First, two from Clive Palmer's Palmer United Party, the Democratic Labor Party's John Madigan, South Australia's Nick Xenophon and, if he's lucky, one from the Sports Party.

"The new senators won't know what day of the week it is," says a veteran senator.

And how well led will they be? How methodical will Clive Palmer's people prove to be, following a man who has straight-faced made the bizarre accusation that the Electoral Commission is in a conspiracy with the army?

Remember the minority government from 2010 to 2013? "What happened in the House of Representatives under Gillard will be transposed to the Senate under Abbott," projects an experienced Liberal senator, as the Coalition government has to somehow cobble together a majority item by item, bill by bill, vote by vote.

"The government will be run from the Senate." Or, more exactly, the possibilities of the Abbott government will be defined by the limits imposed by the Senate, the chamber that Paul Keating memorably denounced as being "unrepresentative swill."

"The difference" between the Gillard minority in the House and the Abbott minority in the Senate, "is that, say what you like about Tony Windsor and Rob Oakeshott, they were smart and they were reasonable and they were experienced," a Labor MP chimes in.

On the best-case scenario in WA, if the Coalition can hold all its senators, it will need to conjure votes from six of the eight crossbenchers on any issue where it is being opposed by Labor and the Greens.

On the worst case, where it loses one, it will need seven of the eight.

Either way, on the two biggest issues for Abbott, he is likely to prevail. These are the repeal of the carbon tax and the mining tax. If he were blocked in the Senate on these, he'd be forced to consider calling an early double dissolution election to get his way.

But while he might have to do some negotiating, ultimately, on the known personalities and positions, the new senators who will take their seats after July 1 will not stop Abbott from honouring his promise to get rid of the carbon tax and the mining tax.

"These bastards will horse trade," says a government strategist.

"There will be something they want to horse-trade on."

The independent senator Xenophon, respected as an effective and sensible swing vote in the upper house, offers the newcomers this thought: "Avoid horse trading because you might get a donkey, and worse yet you might end up looking like an ass."

Beyond that detail, however messy it might be, the crossbenchers, Palmer party included, are not preparing to frustrate the core business of the new government.

That will be a big relief to the Abbott government. But the point that has been overlooked is that even if Abbott keeps all three of his WA senators, he is nonetheless going to have a tricky time getting his way in the Senate.

Not just because of the itinerants and oddities, Star Wars-like, who will be found wandering the Senate but because of the state of Abbott's own party, the Empire itself.

Abbott will not be able to rely on his own senators, much less the crossbench. Macdonald is only one example of the recalcitrance the Coalition will face from within.

Senators have a long history of defying their party leaders: In the 54 years from 1950 to 2004, 245 members and senators crossed the floor to vote against their own party, or 24 per cent of the parliamentarians who served, according to the parliamentary library.

The record holder, Tasmanian senator Reg Wright*, crossed the floor a remarkable 150 times.

The vast majority of these 245 - nine out of 10 - were conservatives. And they have always been much more inclined to cross the floor when their party has been in power.

The Nationals have six senators, four of them on the back bench, who are always ready to defy their larger coalition partner on their heartland concerns. Other Coalition senators are minded to serve their principles over their parties on a number of key issues.

One early test will be Abbott's vaunted paid parental leave scheme, costing $5.5 billion a year, to be funded by a levy on big companies. This has always been unpopular in the Coalition; it would never have become policy if Abbott had taken it to his party room, which is why he didn't.

But the party will have the final word, and it will be given in the Senate. The government's tentative plan is to put it before the current Senate. Labor will oppose it, but the Greens are open to negotiation. Even if the government and Greens can strike a deal, a core of Coalition senators are determined to oppose it and it will only take five of them to kill it.

Some of the Coalition senators with serious reservations about this bill are Cory Bernardi, Alan Eggleston, Dean Smith and Macdonald. And none of the Nationals like it one bit. They see it as a special favour to high-paid city professionals, a "slap in the face for many rural women," as one put it.

And the paid parental leave scheme is seen as the handiwork of Credlin. Indeed, it has become a proxy for Credlin and the control she wields.

The defeat of Abbott's paid parental leave scheme, says Xenophon, "won't be a double dissolution issue for them, but it will be an embarrassment for them."

After the Howard government lost office, partly a result of overreaching on workplace liberalisation, Abbott told me: "Getting control of the Senate was a curse. It allowed us to do things that we would not normally have been able to get away with, and I think it tempted us to chance our arm in ways which ultimately did us significant damage."

This is one curse from which Abbott is certain to be safe.

Peter Hartcher is the political editor.

*Correction: An earlier version said Reg Withers.