Maine Senator Susan Collins is running for reelection as a moderate — dare we say, “maverick” — Republican who is willing to break with her party on matters of political honor. Her campaign proudly declares that: “Since joining the Senate, Susan Collins has developed a reputation for her ability to work across party lines to create consensus and find solutions to difficult problems.”

Collins likes to position herself as an heir to the tradition of the late Maine Senator Margaret Chase Smith, who stood up to red-baiting fellow Republican Senator Joe McCarthy and delivered her famous “Declaration of Conscience” speech to the Senate in 1950. In that speech, Smith warned that “too much harm has already been done with irresponsible words of bitterness and selfish political opportunism,” and told the leaders of her own party: “I don’t want to see the Republican Party ride to political victory on the Four Horsemen of Calumny–Fear, Ignorance, Bigotry, and Smear.”

If Susan Collins wants to be like Margaret Chase Smith, she needs to make her own “Declaration of Conscience” — and then she needs to act upon it.

Collins has, through a campaign spokesman, urged her party’s presidential candidate, John McCain, to stop making automated “robo calls” into her state that suggest his Democratic rival, Barack Obama, is linked to “terrorists” who “killed Americans.”

A statement from the Collins campaign says: “These kind of tactics have no place in Maine politics. Senator Collins urges the McCain campaign to stop these calls immediately.”

The robo calls, which are being made in Maine, as well as Nevada, Wisconsin and other battleground states, have been roundly condemned by independent observers as vile and dishonest attempts to smear Obama.

So kudos to Collins for distancing herself from them.

But doesn’t she need to speak up, forcefully and in detail about why the McCain campaign’s tactics are wrong? Doesn’t she need to take her party’s nominee to task and say, as Margaret Chase Smith did more than half a century ago: “I don’t want to see the Republican Party win that way.”

And what if McCain does not listen to Collins? What if he and his campaign refuse to halt not just the robo calls but related smear tactics against Obama, who happens to be a colleague of the Maine senator?

If McCain refuses to right the course of his McCarthy-like campaign, shouldn’t Collins quit as his campaign co-chair for Maine?

After all, if McCain won’t take her counsel, doesn’t that defeat the purpose of being a campaign co-chair?

Come to think of it, if McCain doesn’t take her counsel on so clear a question of right and wrong, shouldn’t Collins withdraw her endorsement of the senator from Arizona and back the senator from Illinois? After all, Obama has made it clear that he wants to listen to and work with reasonable Republicans?

If Collins fails to rise to this challenge, Maine voters face a challenge of their own: deciding whether to reelect a senator who talks a good game but does not link her words to actions.

In 1964, Republican members of Congress who objected to the extreme stances and tactics of their party’s presidential candidate, Barry Goldwater, withdrew their endorsements and sometimes switched to backing Democrat Lyndon Johnson. To this day, historians and political players with memories honor men like the late New York Senator Kenneth Keating for putting principle above party in that unsettling campaign season — just as we honor Margaret Chase Smith for putting principle above party at a turbulent turning 58 years ago.

This is another unsettling campaign season, another essential crossroads on the American journey.

Susan Collins, who makes so many claims to independence and integrity, now has a chance to prove that those claims are more than just campaign rhetoric. She has an opportunity to stand in the shoes of Margaret Chase Smith and to be heard as loudly as her predecessor as a principled voice when her party and her nation needs a new declaration of conscience.