If Ontario's Health Minister, David Caplan, was a doctor, he would surely be barred for malpractice. But instead, Premier Dalton McGuinty has continued to keep his most trouble-prone minister in his post, ironically even while shuffling other, more useful members of his cabinet.

McGuinty is keeping alive what to many must appear the biggest mystery in Ontario politics.

Caplan as health minister allowed millions of dollars in excessive payments to be steered to consultants, including political friends, and earlier, as minister responsible for lotteries, he failed miserably to protect ticket buyers from fraud.

Caplan by now should be kaput. Mike Colle, another minister thought to have steered much smaller funds to immigrant groups connected to Liberals, was fired from cabinet, apparently forever.

But McGuinty, who is asked constantly why he keeps Caplan, has replied that he has confidence in, and no plan to remove, him and confirmed this by leaving him out of his latest shuffle.

McGuinty has added, when announcing tighter restrictions on hiring consultants, "the buck stops with me," which sounds contrite and unselfish and some media sycophants have even praised him.

But a government should not be allowed to wipe the slate clean of gross misuse of public money merely by claiming it has brought in a rule to prevent it happening again.

Ontario also had a doctrine called "ministerial responsibility" that meant ministers took responsibility for actions by their ministries and resigned when the faults were considered substantial enough.

McGuinty seems to be abandoning this, although he has not replaced it by promising the premier will resign if substantial faults are found in a ministry.

This also is a province governed by so many rules and procedures that an MPP was almost thrown out of the legislature recently for calling another's comment "disingenuous."

But it has no hard and fast rules on when a minister should resign and would have some difficulties writing any. A rule would find it difficult to draw a line, for example, between a minister wasting millions and one using his government car to pick up groceries.

Some failings by ministers are clearer-cut. A New Democrat, Evelyn Gigantes, in the 1990s blurted out under questioning the name of a drug addict, which violated his privacy, and resigned.

Later, a Progressive Conservative minister, Bob Runciman, resigned after his staff contributed information to a throne speech that identified a young offender, and another Tory minister, Jim Wilson, resigned because an aide revealed that a doctor who criticized government had billed more than most other doctors.

It has since become accepted that a minister who violates privacy laws, even through staff, should resign.

A Conservative minister, Cam Jackson, was forced out after he was accused of spending lavishly in hotels and restaurants, but nowhere in the same league as the payments to consultants. The legislature's integrity commissioner ruled his expenses were reasonable, but too late for him to get his job back.

Some premiers have been more reluctant than others to fire ministers being criticized, because this would admit they made mistakes.

Bob Rae, as NDP premier, became so anxious to prove he would not tolerate anything that sounded like an error he fired Mike Farnan as solicitor general after his staff wrote to a court on his letterhead that a constituent had been given a parking ticket by mistake, although Farnan never saw the letter.

McGuinty has held on longer in trying to avoid losing ministers. He refused for two years to yield to demands he fire Harinder Takhar, who was spotted at his former private business and raised suspicion he still worked there, which is against the rules, and Takhar is still in cabinet.

Whether a premier drops a minister in the end depends mostly on how long he is prepared to hang in and take the heat. But if critics get Caplan's scalp, they will go after deputy premier George Smitherman, who as a previous health minister also approved some questionable spending and is someone McGuinty cannot afford to lose.

This is a battle for high stakes.