– Four Democratic senators who defied President Obama to help defeat gun-safety legislation face the wrath of activists who promise to make them pay a political price.

Obama said it was a “shameful day” in Washington when the Senate rejected a watered-down bill that included expanded background checks for gun buyers on April 17. Several groups say they plan to punish the four Democrats through newspaper and television ads, protests outside their offices and automated telephone calls to constituents.

“The level of anger around this is higher than on anything I’ve seen in years, decades,” said Matt Bennett of Third Way, a policy group aligned with Democrats whose founders previously worked on gun-policy issues.

Three of the senators are up for re-election in 2014: Max Baucus of Montana, Mark Pryor of Arkansas and Mark Begich of Alaska. North Dakota’s Heidi Heitkamp is in her first six-year term. All are from states that voted for Republican Mitt Romney for president last year. And while the outside groups will target both Democrats and Republicans who voted against the legislation, they are particularly angry at the Democrats who broke ranks.

“We’re shocked,” said Po Murray, a spokeswoman for the Newtown Action Alliance, a group founded to press for stricter gun laws after 20 schoolchildren were killed in Newtown, Conn., on Dec. 14. “We can’t believe those whom we’ve elected to protect our life and liberty would choose special interests instead.”

Even though the measure was blocked, the debate about gun control has changed from where it was for almost 20 years, when many Democrats avoided the topic altogether. The last major gun-related law was a 1994 crime bill that included an assault-weapons ban. Democrats lost control of Congress later in the year amid opposition to that and other initiatives. The ban lapsed in 2004.

Still, political observers expressed skepticism that the groups’ efforts would succeed in mostly rural states with a strong gun culture.

“In fact, some of these groups going into these states probably helps them,” said Jennifer Duffy, a Senate analyst at the nonpartisan Cook Political Report in Washington.

Baucus, chairman of the Finance Committee, said his “employers are the state of Montana,” when asked about breaking with fellow Democrats.

Said Begich after the vote: “I voted what has been consistent with where I have been for the last 25 years.”

Heitkamp told the Dickinson Press that her constituents indicated 5-to-1 opposition to the legislation. “This was what North Dakotans believe,” she said.

Pryor’s office didn’t respond to a request for comment.