Sen. Roy Blunt (R-Mo.) talks to reporters after a Republicans strategy session at the Capitol in Washington. (J. Scott Applewhite/AP)

On Thursday she voted for it, as did every Republican in the Senate save her home-state colleague, Olympia Snowe.

The amendment introduced by Sen. Roy Blunt (R-Mo.) gained support and attention as a response to the health-care bill’s birth-control cov erage mandate. But the language was not that specific, and Democrats hammered on the issue in competitive Senate races (just look at this ad). Polls suggest the public supports a compromise from President Obama that would keep Catholic employers from directly paying for contraceptives.

Controversial legislation with little chance of passage is usually where moderates and vulnerable senators show their independence. Sources say that Senate leadership did not pressure their members on the vote.

“Leadership realized too late that the Blunt amendment was too broadly written and we should just let it go,” said a Republican aide. “When this initially broke, by making it a religious liberty issue, we were winning the debate. But after the White House came out with their so-called compromise, our side lost hold of the narrative and it slipped back to an issue of women’s health and contraception rather than religious liberty.”

Yet Collins, along with fellow moderate Sens. Scott Brown (R-Mass.) and Lisa Murkowski (R-Alaska) and vulnerable Sen. Dean Heller (R-Nev.), all voted for the amendment.

Both Democrats and Republicans say that those votes suggest that the issue is more important to the GOP base than people realize.

“I think this vote was notable in that almost all of the GOP conference stuck together,” said another Republican aide, noting that three Democrats joined them, “despite the amount of money spent on the other side and the extremely hyperbolic and misleading rhetoric that arose on this issue.”

Republicans also argue that in more conservative states, it will hurt Democratic candidates to be tied to liberal senators on this issue.

“Republicans can only hope that Chuck Schumer travels to North Dakota, Nebraska, Missouri and Montana this Fall, campaigning side-by-side with each of their Democratic candidates and explaining to voters why government mandates should take precedence over the Constitution,” said National Republican Senatorial Committee chairman Brian Walsh.

They point out that even in Massachusetts, a former Democratic mayor of Boston backed Brown on the amendment, and the senator is currently gaining in polls.

Democrats counter that this issue is a winning one for them across the country, comparing it to stem-cell research in 2006. (They’ve gotten a boost from the involvement of Rush Limbaugh, who called a woman who testified in favor of the mandate a “slut.”)

Who’s right? We’ll know in November.

This post has been updated.