As one might guess from my post yesterday, I agree with Steve that one of the main lines of attack on the Cons needs to be that they're the main obstacle to a functional government. But it's worth noting that the Libs will have an awfully tough time trying to justify that argument if they're willing to throw the coalition under the bus.
Let's start by looking to the core of what the Cons have done to make it impossible to get anything done in Parliament. Probably the most obvious problem is their complete refusal to acknowledge that the opposition majority of MPs has any right to make use of its greater number of seats and underlying votes to question the executive power wielded by Harper. And that has led to the Cons shutting down committees and legislative processes as well as pushing this month's prorogation.
Before the coalition came about, the Cons' main complaint about any opposition cooperation was based on the idea that the other parties were ganging up on them, with few specific attempts to divide and conquer. But in the wake of the coalition, they've tried to make an explicit argument that NDP and Bloc MPs shouldn't count in determining what gets done in the House of Commons.
Leaving aside for a moment the problems with that position from a democratic standpoint, it also presents a serious strategic issue - and no less so for the Libs than for the other opposition parties.
After all, in trying to send the message that more cooperation is needed in Parliament, it would seem to make sense as a matter of principle that nobody would be arbitrarily excluded from being involved in that cooperation.
And more importantly, the only way for the Libs to cooperate in a way which doesn't involve giving the Cons effectively what they want is to work with the NDP and the Bloc. In contrast, by conceding that cooperation has to involve the Cons, the Libs would ensure that Harper controls the agenda in Parliament.
Which means that it's a serious problem if the Cons' communications machine goes largely unopposed in claiming that NDP and Bloc votes aren't legitimate when it comes to the coalition. Once that seed is planted by the Cons and either left unchallenged or outright endorsed by the Libs, it'll surely bear fruit for Harper when it comes to other votes. And I can't imagine the Libs will be any better off letting Con actions pass because they accept the Cons' assertion that NDP and Bloc votes can't legitimately challenge a government than they were standing down based on excuses like "Canadians don't want an election".
Now, the Libs might theoretically be able to argue for the legitimacy of NDP and Bloc votes generally while at the same time distancing themselves from the coalition. But that would make it awfully difficult for the other opposition parties to see them as trustworthy, more likely leading to a reduction in the ability of Parliament to function rather than an improvement. And moreover, it would still represent a show of weakness which would enable the Cons to make much of their message stick.
In sum, for the Libs to mount any credible case that it's the Cons who represent the greatest obstacle to a functional House of Commons, they need to be willing to stand up for both the idea that the other parties can work together, and the the most concrete example of that collaboration. And if Harper is allowed to define the limits of what type of cooperation is acceptable, the Libs can rest assured that it's Harper alone who will benefit from the definition in the long run.