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Mr. Wadhams warned that the grass-roots efforts should be prepared for an onslaught of outside cash from gun control proponents like New York Mayor Michael R. Bloomberg, who launched a $12 million ad blitz Monday aimed at gaining support for universal background checks for firearms purchases.

The ad campaign targets 15 U.S. senators, 10 Republicans and five Democrats, who are seen as swing votes on background checks.

“The intensity factor will work in favor of recall proponents,” Mr. Wadhams said. “But look how much money Bloomberg is willing to spend in national races, and think of how much money he could spend on four local recalls.”