John Baird's departure from politics after almost 20 years leaves Stephen Harper in a fix.

The former foreign minister, transport minister, environment minister and Treasury Board president was not only a linchpin in the Conservative cabinet, he also represented a key element in the coalition that has kept this government in power for almost a decade: the Mike Harris conservatives.

As the bond between the Harrisites and the Harperites weakens, the Prime Minister's electoral prospects weaken with it.

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Mr. Harris and Mr. Baird were part of the hard-right Common Sense Revolution that swept to power in Ontario in 1995. Though Mr. Baird, then a rookie MPP from suburban Ottawa, was only 25 on election day, the new premier gave him a series of increasingly important assignments, before promoting him to cabinet in 1999.

"He was whip smart, and a fast learner," Mr. Harris said Tuesday in an interview. "He got better and better every day."

The Mike Harris team, as they liked to call themselves, wanted no truck with the federal Progressive Conservatives, whom they derided as liberals in all but name. But the Reform Party was too socially conservative for their tastes. For the most part, they kept to themselves during the years when the right struggled to unite federally.

The Harris conservatives were impressed, however, by Stephen Harper, who married a strong conservative agenda to a pragmatic appreciation for how to build and grow a winning electoral coalition. They supported and encouraged his efforts to merge the Canadian Alliance, successor to Reform, with the remaining rump of Progressive Conservative MPs.

Like them, Mr. Harper was dedicated to shrinking the size of government, lowering taxes, reducing red tape and balancing the budget. Like them, he realized that marrying such an agenda to what the Republican right calls "God, guns and gays" risked alienating voters who might otherwise support them.

With the Liberals back in power at Queen's Park, Mr. Baird, Tony Clement and Jim Flaherty, who had also been in the Harris cabinet, went up the road to Ottawa in 2006, anchoring a new, weak Conservative minority government otherwise devoid of any experience. To be truthful, they knew more about how to run a government than Mr. Harper himself.

They did more. Although the Harper government is rooted in the West, it is sustained by millions of suburban, middle-class voters in Ontario. Mr. Baird, Mr. Flaherty and Mr. Clement grew up among these voters, understood their values and concerns and translated those priorities to the crew in Ottawa. Along with the former Reformers and Progressive Conservative voters, suburban Ontario voters who supported Mike Harris became the third leg in the new Conservative coalition.

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Mr. Flaherty died last year, and now Mr. Baird has stepped down. Mr. Clement is still in the game, negotiating a contentious new contract with public servants as President of the Treasury Board.

But the old Harris team is breaking up, dissolving decades of historical memory and a bred-in-the-bone sense of what matters to voters in Nepean and Oshawa and Brampton and Burlington and the rest of the vast, Ontario suburbs.

Gerry Butts and Katie Telford, senior advisers to Liberal Leader Justin Trudeau, served at Queen's Park during the Dalton McGuinty years. They have their own sense of how to read suburban Ontario.

This October's election will primarily be a struggle between Conservatives who believe they still understand the soul of the suburban Ontario voter and Liberals who believe they can win those souls over.

Of course, Mr. Harper was himself born and raised in suburban Toronto. He governs in part because he understands those voters as well as he understands the West.

But his team has been weakened. The Conservatives will not be as formidable in Ontario as in previous elections. For that reason, if for no other, Mr. Harper will not be happy with Mr. Baird's departure, and then some.