OTTAWA — Hell hath no wrath like a Conservative government scorned -- just ask the string of bureaucrats, advocates and citizens whose reputations have felt the fury.

Diplomat Richard Colvin is the latest to face a backlash from Tory benches. Conservative MPs at a special House of Commons committee called him a Taliban "dupe" after he provided an account this week of how government officials ignored or played down his reports of the torture of Afghan detainees.

On Thursday, Defence Minister Peter MacKay called his testimony "not credible."

"What we're talking about here is not only hearsay, we're talking about basing much of his evidence on what the Taliban have been specifically instructed to lie about if captured," MacKay said of Colvin's information.

Colvin has been promoted to a senior intelligence job at the Canadian embassy in Washington, D.C., since his time in Afghanistan.

His treatment recalls the public lashing given to another senior bureaucrat, Linda Keen, who drew the wrath of government ministers.

The former president of the Canadian Nuclear Safety Commission was fired after she insisted on keeping the Chalk River nuclear facility closed for safety fears.

At the time, Canada was facing a serious shortage of medical isotopes because of the shutdown and the government had ordered her to reopen the station.

A private letter written by then-Natural Resources minister Gary Lunn questioning Keen's judgment was leaked to the Ottawa Citizen newspaper. And in the Commons, Prime Minister Stephen Harper dismissed the longtime bureaucrat as a Liberal appointee.

"I joined the public service in fact when there was another government in power. I am saying that I am non-partisan," Keen told a special Commons meeting in December 2007, after her appointment was questioned.

"I serve with good behaviour. I have met every requirement of the ethics commissioner and I do my work on a non-partisan basis and I have no political affiliation."

During the last federal election, a Conservative official used a similar partisan tactic on the father of a dead soldier.

Jim Davis had given a television interview where he questioned the government's decision to withdraw from Afghanistan in 2011. A Tory aide circulated an email soon after dismissing those comments by saying Davis had supported then-Liberal MP Michael Ignatieff in the past.

The aide was suspended from the rest of the campaign. Davis' wife called the matter "despicable."

Pollster Nik Nanos says going on the offensive from the start can be remarkably effective.

"It muddies the narrative of anyone trying to criticize the government," said Nanos, who says Tories know the power of first impressions.

"It sends a signal to anyone else who's thinking of doing that, that if you're thinking of taking this government on, be prepared for a full-on offensive. It's a clear media strategy and an effective deterrent for future problems."

Other examples of people who had their credibility attacked by the Tories include:

• Journalist and author Tom Zytaruk. He was publicly accused of doctoring tapes of an interview he conducted with Harper about the late MP Chuck Cadman. Zytaruk, who wrote a book about Cadman, had asked the prime minister about whether the party had once offered Cadman money to step aside from his riding.
• Environmental activist Matthew Bramley. The climate-change director at the Pembina Institute has been dismissed as a Liberal partisan because he provided climate modelling and other advice to former Liberal governments.
• University of Toronto criminologist Anthony Doob, often quoted in the media, has been criticized because he donated to his local NDP candidate in the 2006 election.