WASHINGTON, Mich., June 8 — The undoing of the immigration bill in the Senate this week had many players, but none more effective than angry voters like Monique Thibodeaux, who joined a nationwide campaign to derail it.

Mrs. Thibodeaux, an office manager at a towing company here in suburban Detroit, became politically active as she never had before. Guided by conservative Internet organizations, she made calls and sent e-mail messages to senators across the country and pushed her friends to do the same.

“These people came in the wrong way, so they don’t belong here, period,” Mrs. Thibodeaux, a Republican, said of some 12 million illegal immigrants who would have been granted a path to citizenship under the Senate bill.

“In my heart I knew it was wrong for our country,” she said of the measure.

Supporters of the legislation defended it as an imperfect but pragmatic solution to the difficult problem of illegal immigration. Public opinion polls, including a New York Times/CBS News Poll conducted last month, showed broad support among Americans for the bill’s major provisions.