Premier Dalton McGuinty’s cabinet is seeing an exodus of ministers, but it is not simply a case of rats leaving a sinking ship.

McGuinty’s Liberals have suffered from scandals and are down in polls, deservedly, and are no longer assured of winning an election in 2011.

But ministers — and this is no defence of them — are quitting at least partly for other reasons. George Smitherman, who left as deputy premier and minister of energy and infrastructure to run for mayor of Toronto, would have been a target of huge criticism if he had stayed in cabinet and hurt it as a whole.

Smitherman, 45, had a creditable career in several provincial roles, but in an early one as health minister was among those who bungled an attempt to create an electronic health records system and allowed huge waste.

Since opposition parties forced the resignation of a more recent health minister, David Caplan, and were honing in on Smitherman, he will be relieved to move where he does not bear that burden and government must be glad that he has taken his troubles with him.

Smitherman also would have had difficulty becoming premier, because he is gay, and being mayor of a jurisdiction with nearly one-fifth of the province’s population and no one to give him orders has its attractions.

Michael Bryant, who held posts including attorney general, traditionally the top job after premier and treasurer, quit at 43 because McGuinty does not appear to be preparing to resign, resented Bryant showing eagerness to succeed him and even demoted him.

Jim Watson, 48, who left as municipal affairs minister hoping to return to his former job as mayor of Ottawa, must have felt out of touch with current demands in that portfolio.

Watson brought skills in publicizing. For example, while consumer services minister, he permitted restaurants to allow diners to bring their own wine, which attracted huge publicity and diverted attention from more pressing problems, but whose impact was trivial.

But Watson proved reluctant to tackle serious issues, such as the need to ban municipal councillors from accepting donations from developers attempting to influence their decisions. This ban so far exists only in Toronto.

Watson pointed out that MPPs are allowed to accept such donations but, among many flaws in this argument, they are not the ones who judge most applications for development.

Watson claimed that many in Ottawa’s municipal politics encouraged him to return, and it may be because they felt he would be less of an obstacle to progressive legislation.

Gerry Phillips, a minister without portfolio who recently took on Smitherman’s infrastructure and energy duties temporarily, has been reported as leaving, but his case is different from the others.

Phillips is 68 and was a minister under premier David Peterson in the 1980s who had such stature, when he decided to run for leader more than a decade ago, that he had the support of half the Liberal caucus.

But he withdrew because of a heart problem and asked to be a minister without portfolio because of his health, and has won six elections and would not leaving because he feared losing.

MPPs have left the legislature before an election believing their party would not win. The biggest exodus was before the 1985 election, when the Liberals had not won government in 42 years and a poll rated new leader Peterson the least known of the three party leaders.

Sheila Copps, Don Boudria, Eric Cunningham and Albert Roy, all of whom were certainties to be ministers in a Peterson cabinet, switched to run federally and the first two won and became ministers and the others lost and disappeared from elected politics.

Two of the most worthy New Democrats, Richard Johnston and Michael Breaugh, who had paid their dues and even run for leader, dropped out before the 1990 election never dreaming Bob Rae would lead their party to victory.

One comfort is that those whose political lives depend on it have the same difficulty predicting election results as the rest of us.