"For the past couple of years, I haven't had confidence in the leadership and that was widely known within the party and within caucus," Tom Osborne, the long-serving member for St. John's South, said in an interview.
His doubts stem back to late 2010 and early 2011 when former premier Danny Williams suddenly quit politics and Dunderdale stepped in for what was supposed to be an interim period, he said. When none of the more obvious contenders stepped forward to replace Williams, Dunderdale said she would run for the job.
"I had made that known within caucus that I couldn't support her, and encouraged people to try to persuade somebody else to run," Osborne said.
He declined to go into more detail, but said he has grown increasingly uncomfortable with Dunderdale's tight grip on communications.
"The party has a very well-oiled machine and any time something happens that the premier or the government need to be defended, we would all get pins and emails telling us what to say and how to say it and how to defend the premier."
Osborne also said he has chafed under the government's centralized control and that he regrets voting for contentious Bill 29 last June. Opposition members held a record-long filibuster as access-to-information watchdogs described the legislation as a disturbing rollback on access to cabinet and other documents.
Osborne said he was told there would be repercussions if he voted against the bill, and ultimately decided that it would be better to toe the government line than risk his constituents' interests by isolating himself in caucus.
Since that "turning point" many of those same constituents have urged him to break away from the party, he said.
Asked whether he thinks there will be other defections, Osborne said he could only speak for himself.
"Whether others will make this decision, I'm not sure. It was a very difficult decision to make being involved with the party for such a long time."
Osborne, 47, recalled his early start in politics as a seven-year-old Tory volunteer.
He said he'll consult with his constituents about his political future and may join either the Liberals or New Democrats.
Many voters made it clear to him last fall on doorsteps that they were voting for him personally — not for the party or the premier, he said. He was first elected in 1996 and was a senior cabinet minister holding the justice and health files for Williams.
Dunderdale spokeswoman Lynn Hammond said late Thursday that the premier would not be commenting.
But Steve Kent, the Tory member for Mount Pearl North, said in an interview that Osborne has not been fully engaged in caucus debate for some time and that his departure is not a surprise. Kent said he's more baffled that Osborne is staying in provincial politics, and he poked holes in his rationale for defecting.
"We're talking about somebody who ran under our party's banner and ran for our premier less than 12 months ago. And yet, he can make a statement today that he hasn't supported our premier since the beginning. It makes no sense whatsoever.
"I find that rather frustrating. And then to go on to say that he didn't support Bill 29 when I watched him stand in the house of assembly ... weeks ago and vote in favour of the bill. I'm having a hard time buying some of the story that's being conveyed today."
Kent said he has never been muzzled by party brass and did not speak with the premier's office before offering his views on Osborne.
"I can tell you that our caucus is fully behind Premier Dunderdale."
Osborne's move means there are now 36 Tories in the provincial legislature compared to six Liberals and five New Democrats.
New Democrat Leader Lorraine Michael said he is welcome to join her party.
She described Osborne as a constituent's politician who must have felt intense pressure to go against his conscience on Bill 29.
Still, he has acknowledged with integrity that he can't continue on that path, she said.
"The one thing about Tom Osborne is that he has always shown that he's an excellent MHA and is always there for his constituents on every level.
"So I think he's really being true to himself when he says that he wants to consult with his constituents."
Dunderdale's popularity has consistently eroded in recent polls but still remains higher than her political rivals.
Osborne's bombshell has made for some interesting political times, Michael said.
"I think that's something the premier has to deal with, and she will either see this as part of a bigger problem or she'll ignore it."
Note to readers: CORRECTS to drop extra word in paragraph 4.