Alarmingly for the Coalition, it predicts that for the first time since the Senate was expanded in 1990, it is in danger of not securing three Senate spots in any state. This could influence the NSW Nationals who are still deciding whether to run a separate ticket to the Liberals in NSW. Their lead candidate, Perin Davey, is at number three on the joint ticket, behind Liberals Hollie Hughes ad Andrew Bragg.

The polling sampled the Senate voting intentions of 2019 voters over the past month.

Just four of the current 11-member Senate crossbench are on six-year terms, meaning they are guaranteed to be around after the election and part of the new Senate that takes its place on July 1.

​These are One Nation leader Pauline Hanson, Australian Conservatives Cory Bernardi, and the Centre Alliance's Rex Patrick and Stirling Griff.

Before Christmas, all told The Australian Financial Review they were hostile to Labor's tax policies. None would support the franking credit change while Centre Alliance suggested it would be better to restrict the number of properties that could be negatively geared, rather than confine the practice to new houses only, as Labor plans to do.

The Australia Institute polling indicates that One Nation could expand its numbers from two to four by winning spots in NSW and Queensland and keeping its Western Australian Senator Peter Georgiou.

This is despite the One Nation Senate vote falling from 13.2 per cent in the last poll in March 2017, to 7.9 per cent now.

The poling predicts Centre Alliance could expand its numbers by one, as it is in contention for the final Senate spot in South Australia.

Neither an expanded Centre Alliance nor One Nation would assist Labor's tax plans.

Labor's best hope for a policy ally on the Senate crossbench could be Tasmania, where independents Jacqui Lambie and Craig Garland are competitive with Labor and the Coalition for the final seat there.

The polling sampled the Senate voting intentions of 2019 voters over the past month.