Elizabeth Witmer's resignation means the Ontario Liberals could regain their majority government and deal Tim Hudak’s Progressive Conservatives a crippling blow. (CP)

Within a year of the 2011 provincial election, the Ontario Liberals could regain their majority government and deal Tim Hudak's Progressive Conservatives a crippling blow.

The resignation of Kitchener-Waterloo PC MPP Elizabeth Witmer gives Dalton McGuinty the opportunity to eke out the slimmest of majorities. If the Liberals can win the seat, it would put them and the PC and NDP opposition at 53 seats apiece, a tie broken by Liberal Speaker Dave Levac.

Witmer, 65, had held the riding (and its predecessor) since 1990. Her resignation comes after accepting the Liberal appointment to the Workplace Safety and Insurance Board, a position that comes with a pay increase and increased responsibility.

A former cabinet minister, Witmer was seen as a "heavyweight" within the PC caucus who hailed from the more moderate wing of the party. When Witmer came up short for the party leadership in 2002, she supported Ernie Eves (who, more recently, criticized Tim Hudak's leadership). She gave her support to John Tory in 2004, rather than the more conservative Jim Flaherty, while she stood behind Christine Elliott in 2009 - and not Tim Hudak.

Though she says her decision to accept the Liberal appointment has nothing to do with Hudak's leadership, she is known to have been at odds with caucus on a number of issues. Regardless of whether her departure is a direct test of Tim Hudak's stewardship, the by-election she has caused certainly will be.

Kitchener-Waterloo has voted for Elizabeth Witmer for so long that it is difficult to determine whether the riding is a Tory seat or a Witmer seat. Her vote has been stable over the last three elections at between 41 and 43 per cent, with the Liberals taking 36 per cent last year.

At the federal level, the riding has been one of the closest in the country over the last two elections. The Conservatives won it by a mere 17 votes in 2008, while 2,144 votes separated Conservative Peter Braid from Liberal (and former MP) Andrew Telegdi. Such a close race during the last election, one in which the federal Liberals posted their worst result ever, seems to indicate that the Liberal brand is still relatively strong in the riding.

This means the riding is probably up for grabs, and if the Liberals can find a good candidate they will be able to push the idea of electing a cabinet minister in a majority government. Compared to the idea of electing another opposition MPP, that might be a strong argument.

But what of the NDP? Though they took less than 20 per cent of the vote in the riding in the last two elections, they could play the spoiler. The New Democrats are up in the polls and could steal a good deal of votes away from the McGuinty Liberals. They will certainly try, as every party has a lot riding on the results.

For the Liberals, a majority is at stake. Though it would be precarious (a death or sudden resignation would plunge the party back into minority territory), it could potentially keep the party in power until the 2015 election. For the New Democrats, their bargaining position in a minority legislature could be lost. Though the NSP will be gunning for a victory of their own to cement recent momentum, a PC victory would serve them just as well. And Tim Hudak desperately needs one. His leadership is already on the rocks, and if he presides over the return of a Liberal majority government he may not survive.

Éric Grenier taps The Pulse of federal and regional politics for Huffington Post Canada readers on most Tuesdays and Fridays. Grenier is the author of ThreeHundredEight.com, covering Canadian politics, polls, and electoral projections.

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• Recent Federal Floor Crossers

  <a href="http://www.huffingtonpost.ca/2012/01/10/lise-st-denis-ndp-join-liberals_n_1196406.html?ref=canada-politics">Lise St-Denis' defection from the NDP to the Liberals</a> has put crossing the floor back in the news. Here's a list of other recent federal floor crossers.

• Lise St-Denis

  The newly elected NDP MP jumped ship to the Liberals just 5 months after the federal election of 2011. St-Denis faced harsh criticism from those who saw the move as disregarding the will of her constituents. Many argued that voters in St-Denis' Quebec riding had voted for Jack Layton and not for her.

• Belinda Stronach

  In 2005, Belinda Stronach, Conservative MP and daughter of billionaire Frank Stronach, crossed the floor and joined Paul Martin's Liberal Party. She was named Minister of Human Resources and Skills Development and Minister responsible for Democratic Renewal.

• David Emerson

  In 2006, Liberal MP David Emerson joined the Conservatives just two weeks after being elected. He was named Minister of International Trade and Minister for the Pacific Gateway and the Vancouver-Whistler Olympics.

• Wajid Khan

  In 2007, Wajid Khan jumped from the Liberals to the Conservatives after then-Liberal leader Stéphane Dion stated that Khan would not be permitted to continue in his role as an advisor to Stephen Harper.

• Carolyn Parrish

  Carolyn Parish was suspended from the Liberal caucus in 2004 after stomping on a George Bush doll for a "This Hour Has 22 Minutes" sketch. The outspoken MP subsequently decided to sit as an independent.

• Keith Martin

  In 2004, Canadian Alliance MP Keith Martin renounced his party to sit as an independent and announced he would seek to run as a Liberal in the next election. His move was a response to the merger between the Canadian Alliance and the Progressive Conservatives. He would go on to win the Liberal nomination in his riding and the election and sat in the Liberal caucus until his retirement in 2011.

• Bob Rae

  While Bob Rae isn't technically a floor crosser (he didn't switch parties while sitting as an MP) the interim Liberal leader did switch parties. Rae governed Ontario has the province's NDP premier from 1990-1995. In 1996 he resigned as leader of the Ontario NDP and in 1998 resigned from the party altogether. He returned to politics in 2006, joining the Liberal Party and running for its leadership. He was defeated in his leadership bid by Stéphane Dion, but won the federal riding of Toronto Centre in 2007.

• Ujjal Dosanjh

  Ujjal Dosanjh shares a similar story to Bob Rae. He served as NDP premier of B.C. from 2000-2001, but later joined the federal Liberals. He served as an Liberal MP from 2004 until his defeat in the most recent federal election.