The government is “approaching this term with optimism”, according to the governor-general’s speech opening parliament. This is good to hear, because a more pessimistic character than Malcolm Turnbull surveying the outlook might be in deep gloom.

Labor, the Greens and some other crossbenchers are muscling up against the same-sex marriage plebiscite. Bill Shorten is set to make trouble on most fronts whenever opportunity knocks.

The non-Green Senate crossbenchers, who will be crucial to many of the government’s legislative efforts, find themselves – thanks to their potential power as well as the 24-hours news cycle – receiving continuous attention and publicity.

In a dramatic backbench revolt, conservative Liberal Cory Bernardi has signed up all but one of the Senate Coalition backbenchers and seven crossbenchers – a total of 20 – to a private member’s bill seeking to amend Section 18C of the Racial Discrimination Act to remove “offend” and “insult”. The only backbencher who didn’t formally endorse the bill was new Victorian senator Jane Hume, who has indicated she will support it.

This is a highly provocative jab at Turnbull – who has said changing 18C isn’t a priority – given the timing and number of Coalition backbenchers involved. It’s also said that some ministers, who were not asked to sign, have expressed private sympathy with the bill.

Parliament has started against the background of a Newspoll – the poll Turnbull invoked as a measuring stick when he challenged Tony Abbott – showing dissatisfaction with Turnbull on 52% compared with his satisfaction level of 34%, and Coalition and Labor on 50-50 in the two-party vote.

Not that people are enamoured of Shorten – 36% were satisfied with his performance and 50% dissatisfied.

The ratings for the leaders reflect the public’s general feeling of discontent.

And why wouldn’t people be sick of politics as it is being played?

Take a couple of indicators thrown up by polls published on Tuesday.

Newspoll asked people to say which items from a list they thought the government had a mandate to do.

The results were: maintain border security, 76%; reduce debt and deficit, 75%; meet Australia’s carbon emissions reductions target, 58%; restore the construction industry watchdog, 56%; introduce the superannuation reforms announced in the budget, 54%; resolve the gay marriage debate, 53%; amend Section 18C, 51%. All except the last were election commitments.

Yet despite majorities thinking the government has mandates on these issues, some are still being highly contested. Labor continues to resist bringing back the construction watchdog, and Liberal conservatives are trying to change the superannuation measures.

Admittedly “mandate” theory is a vexed area, and can be argued every which way. The Senate, where governments can rarely get a majority, can legitimately claim its own mandate. Crossbenchers often insist they have (mini?) mandates from those who have elected them, especially now that so many people are disillusioned with the major parties.

This is all very well. But if the mandates of all players are effectively seen as equal, and the numbers and will to routinely block measures are there, this threatens a gridlock that is likely to reinforce public cynicism.

It’s a matter of degree. No-one would expect that a government would get everything through just as it wanted. The Senate has an important checking and reviewing role. But it is reasonable to think a government should be allowed to pass key measures it took to a just-held election.

In some circumstances – such as after the 2014 budget – the public will be pleased when there is obstruction. Other times, people are likely to conclude that parliamentary games are thwarting the public’s will.

Same-sex marriage is a case in point. The Essential poll asked several questions, the results of which collectively said people wanted the issue decided by a plebiscite and would vote yes.

Asked how they would vote if the question in a plebiscite was “Do you approve of a law to permit people of the same sex to marry?”, 57% said “yes” and 28% “no”. Interestingly, 48% said they would definitely vote even if voting was not compulsory, while another 24% would probably vote. On whether the vote would pass, 47% predicted it would, 24% thought not, while 30% were not sure.

People were also asked whether the issue should be decided by parliament or a national vote – 59% said there should be a national vote and 25% wanted it decided by parliament.

Yet the public’s preference is not getting much of a look-in during the current debate. The establishment of the plebiscite will be torpedoed unless the opposition does a U-turn from its very strong rhetoric against it. Labor is trying to force a parliamentary vote – Shorten will bring forward a private member’s bill. Three lower house crossbenchers – independents Andrew Wilkie and Cathy McGowan, and Green Adam Bandt – are also putting up one.

Is trying to frustrate the plebiscite different from, say, the Senate refusing to pass some of the 2014 budget measures? It can be argued that it is. There was not a mandate for measures seen to breach promises or for which there had been no pre-election notice.

The plebiscite was Coalition policy. It might not be the best way of resolving this issue – indeed, I don’t think it is – but it was what Turnbull pledged and what the people favour.

Abbott got into trouble for breaking promises, and now Turnbull is being condemned for attempting to keep one.