They have committed a series of unforced tactical errors, underestimated the resilience of their opponents, misread the public mood and ignored important lessons from past elections. By adopting centrist policies to better challenge for power, they have compromised party doctrine, their position as the nation's social conscience and their credibility with voters.One month ago, Thomas Mulcair's New Democrats were widely favoured by pollsters, pundits and the public to win the most seats in the Oct. 19 federal election. They are now in third place in most polls, and at risk of returning to the House of Commons with fewer seats than the party won in 2011.The NDP's slide has come as a surprise to many, but it shouldn't have. The seeds of decline were evident in August and, in an 11-week campaign, it was only a matter of time before problems would emerge.The party's troubles began, ironically, with Rachel Notley's victory in Alberta in May, which assisted the federal party's ascent to the top of the polls. The mistake was in believing the "Notley effect" had staying power. That assumption spawned two additional mistakes: an oddly low-key performance by Mulcair at theMaclean's debate, and the release of an unambitious platform — the cornerstone of which was the solemn commitment to deliver four consecutive balanced budgets.It was a classic "play it safe" front-runner strategy, but it was a miscalculation. By shifting to the political centre in hopes of assuaging voters' concerns over whether the NDP can be trusted with the nation's finances, the party exposed its left flank. That created an opening for the Liberals to exploit.The Grits quickly shifted from promising balanced budgets to committing to three years of deficits in order to fund infrastructure investments — a position buttressed by polling data showing strong support for such an approach. Since then, Liberal Leader Justin Trudeau has made a series of social spending commitments the NDP's newfound fiscal conservatism cannot match.The NDP should have anticipated the Liberals would move to the left. It was the strategy Kathleen Wynne's Ontario Liberals used last year en route to winning a majority government, and the people who ran the Wynne campaign are running the Trudeau campaign.Beyond that, Team Mulcair should have realized the party's economic platform would alienate many Quebec progressives who are already weary of the Couillard government's austerity measures.Several additional errors have compounded the NDP's problems. Mulcair's defence of the NDP's Sherbrooke Declaration, which would permit Quebec to separate if a secession referendum received "50 per cent plus one" vote, has cost the NDP votes outside Quebec, while his rejection of a niqab ban at citizenship ceremonies has put him at odds with the majority of Quebecers who support the concept.Mulcair's condemnation of Trudeau's promise to cancel plans to purchase F-35 fighter jets contradicts the position taken by former NDP leader Jack Layton and aligns the party with the Harper Conservatives. This week's revelation Mulcair is already planning to run a minority government displays an arrogance, and perhaps a disconnect with reality, that offends many voters.In short, the NDP took the party's base (particularly in Quebec) for granted, underestimated Trudeau and the Liberal campaign, and misread the public's desire for meaningful change. It is now paying the price for those mistakes.Riding high in the polls, and tantalized by the prospect of forming government for the first time, the New Democrats focused too much on defeating the Harper Conservatives, and too little on the threat posed by the Liberals.They adopted a fiscal platform that could have been torn from a Chretién-era Liberal red book, and arrogantly assumed their base would follow them. They never anticipated the Trudeau Liberals would craft a platform that could have been authored by Layton.In an election in which roughly 65 per cent of voters want change and the remaining 35 favour the status quo, the NDP has strayed into the mushy middle, offering a tepid plan that satisfies neither group of voters.Whether the consequence of hubris, gross tactical negligence or both, the party is in trouble — and, with just 17 days before voting day, time is quickly running out to fix the problem.It may already be too late.Deveryn Ross is a political commentator living in Brandon. His columns appear in the Winnipeg Free Press, Westman Journal and several other Western Canadian [email protected]                 Twitter: @deverynross