The Greens have been sitting on the sidelines since December, when Senator Milne cut a deal with Treasurer Joe Hockey to abolish, rather than raise, the debt ceiling.

The environmental party holds several press conferences a day that doubtless delight its base but which make demands to which the Abbott government, nor the Labor opposition, would mostly never agree.

They have barely been sighted since the debt ceiling deal was done, moving further and further from mainstream political debate.

This has been, in part, not of their making. The government has preferred to try its luck with the crossbench and hoped that Labor will support economically responsible measures.

But with Labor leader Bill Shorten determined to replicate the Tony Abbott opposition playbook and with the PUP's Clive Palmer giving new meaning to the word ''unpredictable'', an opportunity exists for the Greens leader to re-enter the political process.

Milne's request for meetings with Labor and the crossbenchers over alternative budget savings is a start.

The idea is simple enough: bring the opposition parties together and find common ground, if possible, and then put any agreed proposal to the government.

The bigger test will be whether Milne will meet Hockey and other senior government ministers to talk turkey over compromise.

An obvious compromise exists, for example, on the proposal to restart fuel excise indexation.

Now all of the $2.2 billion that would be raised by the measure is hypothecated to road spending. Why have not the Greens suggested a compromise deal that would allocate a quarter of that money for public transport or bike paths?

As the government's attempt to force through contentious budget measures has foundered, ''compromise'' and ''adjustment'' have become Canberra's watchwords.

An opportunity exists for someone, anyone, to steer a middle path.

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