I’ve always maintained that Kevin Rudd was unlikely to call an early election, and particularly unlikely to call a double dissolution. Rudd is a natural conservative, a low-risk player, and early elections are a risky strategy. Moreover, being a conservative, having a hostile Senate doesn’t worry him all that much: he’s not wedded to any reformist legislative agenda (he’s a bureaucrat, not a law maker), and the lack of a Senate majority works as a brake on any radical impulses within the government.

That assessment, however, looks a bit less secure this week in the light of the government’s decision to push its legislation on the private health insurance rebate to the front of the legislative queue, setting it up for use as a double dissolution trigger.

Whether that means an early election or not is to some extent a terminological question. If “early” means “before the middle of the year”, the answer is no: a double dissolution before June 30 would backdate the new Senators’ terms to July 1, 2009, throwing out the timing of Senate elections in the next term. A regular election would be even worse, since it could only be for the House of Representatives, with a separate half-Senate election required in the first half of next year.

Governments used to be more cavalier about getting the House and Senate out of alignment (Menzies did it in 1951 and 1963). But poor results in half-Senate elections damaged the Holt and Gorton governments, and the vagaries of Senate timing were a major constraint on the Whitlam government. Since then, no government has seriously contemplated a separate half-Senate election.

In the second half of the year, however, things become more interesting.

The third anniversary of Rudd’s election is November 24, so an election two or three months before that — say late August or early September — would not strike voters as particularly early.

But the unique feature of this year’s timetable is that a double dissolution, which is naturally thought of as an “early election” procedure, is still an available option at that time.

The reason is that although the last election was in November 2007, the new parliament did not sit until February 11, 2008 (even politicians don’t like to work over Christmas), and the limitation on when a double dissolution can be called (Constitution s. 57) works by reference to “the expiry of the House of Representatives by effluxion of time” — which only happens three years after it first sits.

So the fact that a double dissolution cannot be called in the last six months of a parliament’s life just happens, this year, to not be a very serious limitation. The two houses could be dissolved as late as August 10, for an election on maybe September 18. (For much more about the detail of timing, see Antony Green’s careful explanation:

If Rudd decides that the advantages of boosting the minor party strength in the Senate outweigh the disadvantages, he can do it. Indeed, he can do it even if the coalition comes to its senses on the insurance rebate, since he already has a trigger in the shape of the emissions trading scheme (the original version, not the post-Turnbull one that is still before the Senate — although the consensus is that that is much less politically attractive.

I’m still not convinced that he would want to, but this week’s events suggest he is determined to keep his options open.