It happened to Stéphane Dion; it happened to Michael Ignatieff; it has even happened to Bob Rae.

And now the Conservative "war room" has set their sites on NDP leadership frontrunner Thomas Mulcair.

On Thursday, the Conservative party leaked a somewhat suspicious story the National Post, claiming that Mulcair was close to joining the Harper Conservatives after quitting Jean Charest's Liberal government in Quebec in 2007.

A Tory insider told the Post, that Mulcair demanded a Cabinet post as the price for him joining the party - a price Prime Minister Stephen Harper was apparently not willing to pay.

Mulcair calls the story "transparently false."

In an email to the Post, the Quebec MP acknowledges he spoke to the Conservatives (and the Liberals and the Greens) before opting to join the NDP.

"[The Conservative's representative] said the environment was their weakest suit in Quebec and he'd like to know if I'd accept work on that file," Mulcair wrote.

"The Conservatives offered me two senior positions, one as head of a federal agency in environment and the other as a senior advisor. As you can see I took neither."

Mulcair added that he refused the offers because he disagreed with the party's position on the Kyoto Protocol.

Not coincidentally, the story was leaked on the same day the NDP leadership voting began.

Political analyst, Lawrence Martin suggests this shows the Tories are afraid of a Mulcair led NDP.

"This becomes a whose version do you believe type of thing and it could damage Mulcair's prospects of becoming leader. Other NDP challengers will make hay, despite the dubious source behind the story," Martin wrote in a column at Ipolitics.

"Had the Conservatives wanted Mulcair to win this thing, they wouldn't have bothered. They would have let sleeping dogs lie. This clearly shows that they don't want him to win."

Being attacked by the big blue Tory machine has become like a right of passage.

Welcome to "the bigs" Mr. Mulcair.