If there's one Canadian who's paying close attention to the fate of the Tory election promise on income splitting, it's Steve Wellburn.

Wellburn and his wife Tanya allowed the Conservatives to use their Vancouver Island home – and their family – as a backdrop during an important 2011 federal campaign stop.

Neighbours peered out the windows as TV cameras, reporters, political fixers and local candidates descended on the Wellburn backyard to hear about a key plank of Stephen Harper's platform.

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And the Wellburns were the perfect example of a family that would benefit the most from the plan to allow couples with children to pool and then split their incomes to save at tax time. Steve is a chartered accountant in Victoria, Tanya is a stay-at-home mom with three children.

Now that it appears Harper and Finance Minister Jim Flaherty are having serious doubts about the wisdom of the $2.5-billion promise, Wellburn is watching closely to see what happens.

He – like many in Ottawa – wondered whether Flaherty was just floating a trial balloon when he publicly questioned the advisability of the plan, or actually reflecting a government change of heart.

"I think we'd have to see if there was some alternative proposed that would be comparable and similar before we could make any concrete decision how we feel about it," Wellburn said in an interview.

"If they were just to take it away entirely, I don't think that would be a good policy move for them, just because that was one of their campaign promises."

One could argue that it was Fiona Wellburn who was the first to screw up Harper's script on income splitting – long before Employment Minister Jason Kenney or Flaherty sowed confusion this week with conflicting points of view.

Back in 2011, the rambunctious two-year-old bounced up and down stairs and swiped at Harper's legs with stuffed animals while he was trying to explain how the plan would help Canadians.

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"I've got a couple guys whacking me from behind. They're usually packing a bigger punch but they're usually just as low," he quipped.

Fast-forward three years, and the Wellburns have moved to a new house, and are living in Green party Leader Elizabeth May's riding.

The Wellburns are not Conservative party members, but Steve says they've been supportive of many of Harper's policies.

Still, the Wellburn vote is not necessarily in the bag for Harper in 2015 – and a key might be what becomes of the income splitting promise.

"We certainly would look at the best party platform that we would believe economically is good not only for us but the country as a whole, and thinking long-term for that," Wellburn said.

"I think we really would have to see what sort of alternative would be proposed to stand in the place of that income-splitting proposal."

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That point of view is the kind that worries some Conservative MPs, who say they campaigned hard on the promise and want to stick by it for their supporters. Kenney voiced that concern publicly on Wednesday.

Harper and Flaherty will be looking for alternatives that satisfy caucus members that the Steve Wellburns of the world won't drift away come election day.