The polls say we're heading for a minority government, possibly Conservative. A question raised over the last few days is whether the Conservatives could govern.While iPolitics columnist Susan Delacourt (my spouse) thinks they can't, Stephen Harper's former Chief of Staff, Tom Flanagan, thinks they've got a good shot at it. Who's right?Regarding the NDP, little need be said. Few people seriously believe Tom Mulcair would prop up Harper. Mulcair has been one of his most vociferous critics, attacking his foreign policy, fiscal policy, social policy, environmental policy, criminal reforms, institutional reforms and governance style.Moreover, for the first time, the NDP has a real chance of forming the government and Mulcair is pulling out all the stops to position himself as the only leader who can rid the country of Harper. There is virtually no chance Mulcair will vote to keep him in office.The more interesting question is around the Liberals. What happens if they are still the third party after the election? There is an argument out there that siding with the NDP to bring down a Harper minority would simply hand Mulcair a majority in 2020.A string of cases suggests this could be true. For example, the Ontario NDP formed an accord with the Peterson Liberals in 1985, then in 1987 Peterson won a huge majority.The Liberal Democrats in the UK suffered the same fate after forming a coalition with David Cameron's Conservatives in 2010. Cameron now rules with a majority. Examples could be multiplied.Conservatives find this line of argument persuasive, as do some non-Conservatives. They think Liberals will not risk giving the NDP a platform to win a majority government. Liberals' celebrated survival instinct will kick in and quickly trump any other considerations.In this view, if Harper sweetens the pot enough, Trudeau will take the bait. One line even has it that Harper might promise to leave, say, after the sesquicentennial celebrations in 2017.I agree that a partnership of any kind with the NDP would carry risks for the Liberals, but I also believe recent events make clear that propping up the Harper government—for any reason—would be far more damaging to Trudeau.Trudeau brought the Liberal Party back from its near-death experience after 2011. In the process, he staked his credibility on more than policy. He sold himself as part of a new generation that will (finally) govern differently.And this has worked remarkably well for him. Over the last three years, thousands of people showed up at events across the country to hear him. Many believe in generational change and renewal; and they want to believe he can lead it.Nor can Trudeau's pitch be written off as empty rhetoric. He has made commitments to change the system that no previous Liberal (or Conservative) leader would even have considered, including fundamental changes to Senate and judicial appointments, and ground-breaking reforms to ensure transparency and accountability.Trudeau has put change and trust at the centre of his brand, and he has done so in opposition to Stephen Harper, who has served as the principal foil for much of Trudeau's self-definition.Were he now to join with Harper to ensure the Conservative government's survival, progressives would see this as a betrayal of the worst kind. It would conflict with everything the Liberal leader claims to stand for. Trudeau's credibility would be gone. I think the early warning signs on this are clear.First, many progressives were dismayed by Trudeau's embrace of Eve Adams. In the end, Liberals may have “held their noses” till it was over, but there is little doubt Trudeau crossed some line here. The indignation should be taken as a warning shot across the bow.Second, on Bill C-51, the security bill, Trudeau attempted to carve out a nuanced position, criticizing the bill forcefully for its weaknesses, while noting its strengths and conditionally supporting it.Few took the Liberal position seriously, including many Liberals. Many saw Trudeau's decision not to oppose the bill as the product of political calculation, rather than the values he claims to defend.Whether or not this was fair or true is not the point. The thing to note here is how many of the people who were inclined to trust Trudeau were also willing to abandon him, once they decided he had sold them out.I think this is where Conservatives like Flanagan go wrong. They assume Trudeau's decision on whether to support Harper would be driven mainly by concerns over the NDP.This underestimate just how angry so many progressives are at Harper and how badly they want him gone. For them, Harper is not just a political opponent, he is the enemy.If Trudeau were to prop Harper up, his concerns over the NDP would seem like pocket change compared to the storm of anger he would provoke among friends and allies. He wouldn't even get the chance to explain his reasons to them.After Eve Adams and C-51, I assume Trudeau gets this.Dr. Don Lenihan is Senior Associate, Policy and Engagement, at Canada 2020, Canada's leading, independent progressive think-tank. Don is an internationally recognized expert on democracy and Open Government. His recent projects include chairing an expert group on citizen engagement for the UN and the OECD; and chairing the Ontario Open Government Engagement Team. The views expressed here are those of the columnist alone. Don can be reached at: [email protected] or follow him on Twitter at: @DonLenihan