WASHINGTON - It's a natural reaction in times of grief: Politicians from both parties offered thoughts and prayers for those killed in San Bernardino. But within hours, social media was awash with pushback from gun-control advocates calling out those who offer prayers without pushing for tighter gun laws.

"Your 'thoughts' should be about steps to take to stop this carnage," Democratic Sen. Chris Murphy of Connecticut tweeted. "Your 'prayers' should be for forgiveness if you do nothing - again."

Murphy, who has been outspoken in pressing for gun-control legislation, added at a news conference Thursday: "Members of Congress don't get elected to send out sympathy tweets."

As GOP presidential candidates and conservative lawmakers tweeted their prayers after the shooting, Igor Volsky, a contributing editor at the liberal website ThinkProgress, started tweeting back how much each had received in campaign contributions from the National Rifle Association, which opposes tighter gun laws.

Volsky said that his Twitter campaign stemmed from frustration with those who "routinely talk about all the thoughts and prayers they're going to send to victims, and yet they do nothing time and time again in terms of actually reducing these things from happening."

The hashtag #thoughtsandprayers quickly was adopted by those venting frustration with the prayerful sentiments offered by those opposed to congressional action on gun legislation.

The New York Daily News expressed the same idea on its front page with the blaring headline: "God Isn't Fixing This" coupled with images of tweets about prayers from GOP candidates Ted Cruz, Rand Paul and Lindsey Graham and House Speaker Paul Ryan.

Soon came a backlash from those arguing that gun-control advocates were sneering at deeply felt prayers.

Paul tweeted that the newspaper's cover was "deplorable. Genuine thoughts and prayers are not political fodder."

Commentary magazine's Noah Rothman wrote that an "ill-advised impulse to discredit the act of prayer" was an example of "how far removed the left has become from majority opinion in the rest of America."