To many New Englanders, Olympia Snowe had come to resemble Marilyn of “The Munsters” TV family. The senator from Maine seemed a normal Northeast Republican surrounded by party leaders sprouting fangs and cooing at bats — but who regarded her as the odd one.

“You can’t be too careful these days,” Herman Munster, a Frankenstein-monster clone, would tenderly advise the wholesome Marilyn. “There are a lot of strange people in this world.”

To the right wing, Snowe was the fiend, the No. 1 RINO (Republican in Name Only) on its hit list. Having apparently tolerated her last neck bite from supposed allies, Snowe has decided not to seek re-election. And so goes another moderate Republican, a dwindling species that once freely roamed the Northeast, Midwest and Northwest.

New England has already lost Senate Republicans Jim Jeffords of Vermont and Lincoln Chafee of Rhode Island. That leaves Scott Brown from Massachusetts and Maine’s other RINO, Susan Collins. Are their days numbered, as well?

Only Brown faces re-election this year. Though still polling strong, Brown faces some challenges unique to Republicans in socially liberal states. His likely Democratic opponent will be the formidable Elizabeth Warren, the brains behind the Consumer Financial Protection Bureau. No angle against Brown will be left on the shelf, we can be sure.

1. The moderate-Republicans-aren’t-as-independent-as-they-say-they-are angle. Recall how Snowe served the Republicans’ unsuccessful campaign to kill the Democrats’ health care reforms by pretending to be interested in compromise. Desperate for a glint of bipartisan support, President Obama wasted months listening to her objections, appeasing them, then being presented with another objection. When Democrats finally gave up, she complained that they were rushing her.

Brown recently co-sponsored the Republican amendment that would let employers deny coverage for birth control (and who knows what else). Brown may or may not have been acting on principle, but voters will be reminded that freed from the tea party yoke, Snowe voted against the so-called conscience clause.

2. The wicked witch angle. Every year, Republican bad boys crown a Miss Liberal Witch, whom they collectively bomb with ridicule, much of it sexist. Past wearers of the pointed hat include Hillary Clinton and Nancy Pelosi. Without a doubt, Warren is Miss Liberal Witch of 2012. Brown won’t do it, but she can count on his right-wing “helpers” turning her into a feminist martyr. (For more on this, consult Rush Limbaugh.)

3. Finally, the Munster family angle. With the Senate majority in the balance, voters will be buying not only the candidate, but also the candidate’s political family. A win for Brown would mean digging up Kentucky Sen. Mitch McConnell’s hopes to become Senate majority leader.

Chafee was also very popular among his moderate-to-liberal constituents, but concern over putting the Senate in Republican hands prompted many of his fans to help elect Democrat Sheldon Whitehouse. When Chafee was campaigning in 2006, he told me, people would drive up in their cars, lower their windows and say, “I really like you, but I can’t vote for a Republican right now.” Chafee has gone on to become Rhode Island governor.

If the presidential candidate is Mitt Romney, Massachusetts voters will be reminded of how their former governor has disavowed them. And whoever the nominee, they’ll surely be hearing from Newt (“I want to shift the entire planet, and I’m doing it.”) Gingrich. He is famous for calling liberal Democrats “the enemies of normal Americans.” Like he would know.

Froma Harrop is a columnist for The Providence Journal.