The extraordinary emphasis until now on the small parties and individuals among the 11 members of the Senate crossbench has conjured up an image of typical parliamentary decisionmaking in which the two major parties and the Greens stake out their position first and then bargain with the crossbench for support. This puts the pressure on the crossbench, which can be seen to make or break government legislation.

That's how it turned out in the last Parliament when Tony Abbott condemned the Senate for being "feral". In fact, Abbott was referring not just to the crossbench but to all those senators, including Labor and the Greens, who were obstructing his government's program. The Coalition, like any government, always wanted to put the heat on the major opposition party rather than the crossbench, because for them that is the main game. That is how two-party politics works between Labor and the Coalition.

But in fact, as the battle over same-sex marriage shows, the reality is not always like that. In this case, the course of events has ensured that the focus is now not on the crossbench specifically but on Labor. This brings attention, but also potential discomfit.

The government laid down its determination to proceed with its policy of a plebiscite. After some general speculation about what everyone else would do, the Greens announced firmly that they would oppose one. Without much media attention it became clear that the Hanson One Nation team, Jacqui Lambie, Bob Day and David Leyonhjelm (a total of seven votes) would support the government. Derryn Hinch would oppose it.

That left the Nick Xenophon Team and Labor. Initially Labor's apparent opposition made it seem as though the three NXT senators would hold the balance of power. But then Xenophon made an early call and confirmed that NXT would oppose a plebiscite.

So now everyone's position is known except that of Labor, which has talked up its opposition in principle but has left open its final position until it sees the detail of the plebiscite bill, including the wording of the proposed plebiscite question. This is similar to its position on the government's omnibus budget repair bill; that is, give an indication of in-principle support but hold off until it sees the detail.

There are two lessons here, one general and one specifically for Labor.

The general lesson is that there will be many different ways in which issues play out in the Senate. Sometimes the major parties will have firm and clear long-standing positions around which the Greens and the micro parties will have to negotiate.

But on other occasions the opposition, and sometimes the government too if they are willing to entertain amendments, will have flexible positions. This will mean that the Greens and the crossbench may find themselves taking the lead.

There are opportunities and difficulties in both types of situations. If the government and Labor have firm positions then the smaller players can take their time making up their minds before bargaining about amendments and seeking special deals. That can bring tremendous pressure and media attention, as shown in the last Parliament. Reputations can be made, but they can also be destroyed.

On the other hand if the smaller players take a lead, as Xenophon and Andrew Wilkie in the House of Representatives have on gambling reform, they can not only make the major parties play catch up but they can also put the pressure back on them. In all these matters, the smaller players are cut some slack because they genuinely have more limited staff and other resources to fall back on in the face of a large government legislative program.

Labor is in a special position. It's expected to have a clear position on everything the government throws at it because it's a big party with extensive resources and established positions across the board. Labor doesn't have the bureaucracy to rely upon, so the government always has an advantage, but expectations are still high.

That is why Labor's positioning on same-sex marriage should be a learning experience. They could have taken the lead and made their opposition to or grudging support of a plebiscite clear at the same time as the Greens and NXT resolved their positions. Instead, they appear to have hardened their opposition to a plebiscite without either definitively ruling it out or supporting it under cover of negotiating a favourable compromise over the wording of the plebiscite question.

This may be a reasonable and measured approach, which may also have the benefit of allowing discussions within the party room. Last-minute support for a plebiscite, announced as being in the national interest after weighing the pros and cons, may indeed be the right thing to do, and if the plebiscite eventually passes will be judged to be the right call.

However, there is a downside because it not only puts Labor in the hot seat for the time being but also means it has to suffer attacks from pro-same-sex marriage Liberals, including Warren Entsch and the newly elected Tim Wilson. There is also a fine line, at least in public perceptions, between a measured approach and dithering indecision.

John Warhurst is an emeritus professor of political science at the Australian National University.