Why now?

The question will dog Sen. Olympia Snowe until that fast-approaching day when, for the first time in almost four decades, she no longer has a title affixed to her household name.

“Unfortunately, I do not realistically expect the partisanship of recent years in the Senate to change over the short term,” Snowe said in a prepared statement that sent all of Maine (and beyond) into a political tizzy late Tuesday afternoon.

“So at this stage of my tenure in public service,” she continued, “I have concluded that I am not prepared to commit myself to an additional six years in the Senate.”

Meaning she’s done. Finished. End of story.

And with Election Day just over eight months away, a U.S. Senate seat that only yesterday appeared as invincible as they come is now up for grabs.

Democratic challengers Matt Dunlap, Jon Hinck and Cynthia Dill can only be pinching themselves right about now. Ditto for Scott D’Amboise, who decided to challenge Snowe in June’s Republican primary because … why?

Then there are those who never dreamed of a 2012 Senate run – Maine Senate President Kevin Raye (who’s already running for Maine’s 2nd District House seat) and U.S. Rep. Chellie Pingree (whose husband, S. Donald Sussman, just saved my job). Will they now hit the reset button and scare up 2,000 signatures by the March 15 deadline to qualify for a ticket to this sudden free-for-all?

All of which brings us back to that nagging question for a woman who long ago became a Maine legend, a perennial winner for whom anything less than 65 percent of the vote was considered an underachievement.

Why now?

It’s easy – and downright tempting – to speculate about what might be lurking behind Snowe’s lament Tuesday that “an atmosphere of polarization and ‘my way or the highway’ ideologies has become pervasive in our campaigns and in our governing institutions.”

Could it be illness?

“My husband and I are in good health,” she said in her statement.

Could it somehow be tied to the ongoing U.S. Department of Justice lawsuit against Education Management Corp., which is chaired by Snowe’s husband, former Maine Gov. John R. McKernan?

Time well tell … or not.

Or could it simply be that Snowe, who has served this state nonstop since she first took the seat of her late husband, Peter Snowe, in the Maine Legislature way back in 1973, has finally had it?

It is, to be sure, a foreign concept in an era when political power is for so many an end rather than a means. But think about it – if the rest of us can retire at age 65, which Snowe turned just last week, why can’t a U.S. senator?

And if the rest of us can turn our backs on what passes for politics these days in Washington, D.C., why can’t someone who built her entire career – sometimes successfully, sometimes not so much – on straddling the ever-widening partisan divide?

Two years ago last fall, Snowe found herself at the center of the bitter debate over President Obama’s health care initiative. I spent a couple of days watching her, as she put it at the time, “at the eye of the storm” raging throughout the U.S. Capitol.

Democrats, including Obama, wooed her – until she ultimately voted the other way.

Far-right Republicans lambasted her as a RINO (Republican in Name Only) for her willingness to even consider what the opposition had to say.

She did admit with a rueful smile, “I never saw it unfolding this way.” But she never faltered.

“I don’t get up every morning and say this is going to be another can’t-do day,” Snowe told me that day. “I get up and think, ‘Is this something we can accomplish today?’“

So one more time … why leave now?

Until someone proves otherwise, I’ll take the senator at her word.

Sad as it may sound, Olympia Snowe has done all she can.

Columnist Bill Nemitz can be contacted at 791-6323 or at: bnemitz@mainetoday.com