While Labor leads in the polls, the unexpected result in 2019 has made everyone cautious about making predictions. Questions surround the possibility of a minority government, the impact of independents in blue-ribbon Liberal seats, and the effect of the United Australia Party. The past two years have only emphasised anything can happen to drastically upturn the world.

But with the focus on the House of Representatives, there's been little attention paid to the Senate, which might have a bigger impact on the agenda of whoever forms government.

In 2019, the Liberal National Party and One Nation won four of six Senate seats between them in Queensland, making a Labor-Green Senate majority almost impossible in 2022. Unless Labor and the Greens do very well this election, it's likely that the Senate will be deadlocked. This means that if Labor forms government, it will likely require support either from the Coalition or (more likely) a combination of Jacqui Lambie, the Greens and One Nation to pass any legislation in the Senate.

For progressives, this has huge implications for legislation on a national integrity commission, climate change or insecure work. The Rudd government's ambitions on climate and industrial relations were stymied by needing the votes of the Greens, Family First's Steve Fielding and independent Nick Xenophon all at the same time (in the absence of Coalition votes). This irreconcilable alliance sowed the seeds of discord for what came later.

A working majority for progressives in the Senate requires a few things to happen. Firstly, Queensland and South Australia need to split evenly and give Labor and the Greens three seats between them in each of those states, a net gain of two seats. Then progressive parties need to either win an extra Senate seat somewhere else, or the Coalition must be denied a Senate spot.

To date, attention has primarily been on the ACT due to their high-profile Senate candidates. Along with the perennial campaign by the Greens, academic Kim Rubenstein and former Wallabies captain David Pocock all launched "climate independent"-style campaigns, all aimed at knocking off Liberal senator Zed Seselja. There are also rumours of more prominent candidates announcing Senate bids in the ACT.

But despite the hype around these candidates, it is hard to see any of them winning. To beat Zed, the Liberal primary vote needs to be dragged into the 20s - while making sure others' preferences flow strongly and do not exhaust. It seems highly unlikely - the lowest-ever ACT Liberal Senate primary vote was 31.2 per cent in 1998, after savage cuts to the Australian Public Service that sent Canberra into a recession.

In short, unless some of these independents pull out of the race, the likelihood of Zed losing his Senate spot is actually decreasing. The only time when more candidates would have helped was under Group Ticket Voting, when all ticket preferences could be directed. That no longer exists.

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Rather than Zed losing in the ACT, either a third Labor senator from Victoria, a second Jacqui Lambie Network senator from Tasmania or a possible returned Nick Xenophon from South Australia seem like the most realistic scenarios. These Senate contests should be grabbing the attention of progressives, as they will likely determine whether key legislation passes.

The Senate deadlock problem is unlikely to go away. The demise of the Democrats has meant the Coalition now reliably wins three Senate seats in most states, and the fall in Labor's primary vote in Queensland has delivered four out of six Senate seats to right-wing parties on more than one occasion.

Outside of double dissolutions and a landslide result in a state, a deadlocked Senate is likely to become a more frequent occurrence without swing seats. A vote of 43 per cent is all that is needed to win half of the Senate seats in a state. Expanding the size of the Senate, potentially by increasing territory Senate representation to an odd number to create swing seats, needs to be given serious consideration.

If there is a change of government, the make-up of the Senate may determine the ambition of a first-term Labor government. For progressives, it reinforces the necessity of being strategic with campaigning, to ensure a working majority in both the Senate as well as in the House.