It's becoming a lot lonelier at the top for Dalton McGuinty

For months, Dalton McGuinty's government has brushed off the exodus of its incumbent MPPs as nothing more than healthy turnover.

Last week, that spin got a little less credible.

Economic Development Minister Sandra Pupatello's surprising announcement that she will not seek re-election on Oct. 6 has some practical consequences for Mr. McGuinty's Liberals - likely costing them one of their best attack dogs during the coming Ontario campaign, and weakening their hold on a Windsor riding targeted by the provincial NDP. But the biggest damage might be to the Liberals' fragile psyche.

Outside of the Premier and his senior campaign team, there is a palpable uneasiness within that party's ranks - much more so, many Liberals concede, than heading into the last campaign in 2007. And Ms. Pupatello's departure plays right into their fears of the end of an era, and a party in decline.

She is not Mr. McGuinty's most senior minister; indeed, she never quite made it to the top-tier role many had expected for her. But she is one of his very best warriors. Nearly as combative from the government benches as she was back in her opposition days, she's a commanding presence that friends and foes alike are reluctant to mess with. And since coming to Queen's Park in 1995, she's been a big part of the Liberals' heart and soul.

That she is heading for the hills before her party's biggest fight has to sting more than the 11 other Liberal pre-election retirement announcements, because nobody saw it coming. But what makes it all the more troubling for her party is that, really, it's perfectly understandable.

Aside from whatever personal reasons Ms. Pupatello may have for leaving - and those should never be discounted whenever politicians seek a less all-consuming line of work - she has plenty of good professional ones.

In fact, the Liberals have reached the point in their reign when many of their more senior MPPs have good cause to consider moving on. If they're worried about making the most of their remaining earning years, and don't have designs on Mr. McGuinty's job, there is more risk than reward in sticking around.

For the most part, they have experienced everything they could ever have hoped to experience in politics. Going out on top means they don't chance the extreme low of losing their seats if the Liberals are swept from office - a distinct possibility, despite their competitive polling numbers. Nor are many Liberals who once toiled in opposition eager to spend another four years there, if they keep their seats but their party loses government.

In such cases, loyalty is one of the best arguments for sticking around. But with the odd exception - Finance Minister Dwight Duncan comes to mind - Mr. McGuinty seems to command a limited degree of it. Although generally regarded as a decent sort, his remoteness makes it difficult for many people to get close to him. And he has a way of marginalizing those who show too much ambition, all but encouraging them to seek greener pastures.

Of the 22 men and women appointed to his first cabinet in 2003, only eight are still on the front benches and expected to seek re-election this fall. And Mr. Duncan, who himself has recently faced some speculation about his future, is just about the only one who has been senior all the way through.

Some Liberals would argue that's renewal, and if they do get re-elected the need to inject fresh talent into cabinet might serve them well. In Mr. McGuinty's second term, a few newer faces have capitalized on the opportunities given to them - notably Health Minister Deb Matthews and Transportation Minister Kathleen Wynne, both of whose names come up in leadership speculation - and others might yet emerge to carry the torch.

But for now, the Liberals' team is starting to look like a shadow of its former self. Mr. McGuinty, at least, still seems very much up for one last fight. But if even Ms. Pupatello is no longer eager to stand alongside him, the Premier must be starting to feel a little lonely.