Come voting day on Oct. 19, both NDP Leader Tom Mulcair and Liberal Leader Justin Trudeau will want you to think of them as the best left-wing alternative to Prime Minister Stephen Harper and the Conservatives.

That’s why Mulcair and Trudeau will be throwing as many haymakers at each other for the next two months as they are at Harper.

In their latest skirmish, the Liberals describe Mulcair’s promise of a national daycare program — one million $15-a-day government subsidized daycare spaces — as a “mirage”.

The Liberals argue Mulcair’s $5-billion promise would require a provincial buy-in of $3.3 billion, which provinces like Ontario, can’t afford.

Plus, they say, the NDP won’t deliver all the spaces until 2023 — two elections away — meaning Mulcair’s pledge is meaningless.

In Ontario, Premier Kathleen Wynne’s government has joined the federal Liberal attack on Mulcair, saying he was wrong to claim Ontario supports his daycare plan.

Finally, they note, under the NDP policy known as the Sherbrooke Declaration, provinces have a right to opt out of federal cost-sharing programs like daycare, take the federal money instead and run their own programs.

Mulcair has fired back he knows the Liberals are frustrated with his popular national daycare plan because it reminds them of their own failure to bring one in when they were in power.

He says he’ll work with Wynne’s government (which supported an Ontario NDP motion last year endorsing a federal-provincial $15-a-day daycare program) and all the provinces to make it happen.

The thing to understand about this Liberal-NDP bunfight is that it has nothing to do with delivering a national daycare program.

Federal governments have been promising and failing to deliver that for decades, dating back to the Brian Mulroney Progressive Conservatives.

The Liberals still complain Paul Martin was about to introduce a national daycare plan in 2005 when Mulcair’s predecessor, the late Jack Layton, pulled the plug on his minority government, leading to its defeat by the Harper Conservatives.

The reason no federal government has delivered a national daycare program is that it would be ruinously expensive (see Quebec’s $7-a-day program) and requires the co-operation of all 10 provinces, making it akin to herding cats.

Finally, many parents (and voters) prefer the Conservative and (in this election) Liberal promise of letting them keep more of their own money so they can decide on appropriate child care for themselves.

In reality, the political infighting between the Liberals and NDP on daycare isn’t about daycare.

It’s about winning the hearts and minds of voters who want a “progressive” alternative to the Harper government.

And it’s just getting started.