WASHINGTON – Supporters of President Obama’s gun control proposals are planning a methodical, state-by-state campaign to persuade key lawmakers that it’s in their political interest to back his efforts to crack down on firearms and ammunition sales and expand criminal background checks.

To succeed will require overturning two decades of conventional wisdom that gun control is bad politics.

The National Rifle Association is confident that argument won’t sell. But with polls showing majorities supporting new gun laws a month after the Connecticut shooting deaths of 20 schoolchildren and six adults, gun control activists say the political calculus has changed.

Their goal in coming weeks is to convince lawmakers of that, too, and to counter the NRA’s proven ability to mobilize voters against any proposals limiting access to guns.

The gun control advocates are focused first on the Senate, which is expected to act before the House on Obama’s gun proposals.

How Senate Majority Leader Harry Reid, D-Nev., proceeds will depend in part on what he hears from a handful of Democrats in more conservative states where voters favor gun rights.

These include some who are eyeing re-election fights in 2014, such as Mark Pryor of Arkansas, Mark Begich of Alaska and Max Baucus of Montana.

“We need to tell our members of Congress that they’ve got to stand up for sensible gun laws, and if they do that, we will stand up for them, and if they don’t we will stand up for whoever runs against them,” New York Mayor Michael Bloomberg told the U.S. Conference of Mayors on Friday. “Because that’s exactly what the NRA is trying to do.”

Bloomberg’s group, Mayors Against Illegal Guns, is among a coalition of 50 labor unions, advocacy groups and others that have been meeting since before Christmas to plot strategy, in loose coordination with the White House, according to people involved.

Just hours after Obama rolled out his gun proposals Wednesday, the group gathered at the headquarters of the National Education Association to game out their plans.

As of Friday, voters’ calls to Reid’s office were running 2-to-1 against Obama’s proposals, a Reid aide said.

Never far from such Democrats’ minds is what happened in 1994, when the party suffered widespread election losses after backing President Bill Clinton’s crime bill featuring a ban on assault weapons. Clinton and others credited the NRA’s campaigning with a big role in those Democrats’ defeats. And when the assault weapons ban came up for congressional renewal in 2004, it failed.

The goal of gun control supporters will be to convince Democrats like Pryor, Begich and Baucus through phone calls, appearances at town hall meetings, print and TV ads and other means that voters in their state will support them if they back Obama’s plans.

One group involved, the Coalition to Stop Gun Violence, ran print ads in North Dakota newspapers criticizing newly elected Democratic Sen. Heidi Heitkamp after she expressed doubts about Obama’s proposals.

Activists have also identified a few Senate Republicans they hope to sway, including Mark Kirk of Illinois and Susan Collins of Maine. In the House, they’re focused on 35 to 40 Republicans in suburban areas or districts carried by Obama, where voters might be more supportive of gun control measures.

But the NRA, which claims 4 million members, has already activated its base, issuing a fiery appeal this week in which Executive Vice President Wayne LaPierre warned backers: “It’s about banning your guns, period! … I warned you this day was coming and now it’s here. This is the fight of the century.”

As publicity spreads about Obama’s proposals the NRA has been adding about 8,000 members a day, according to the group’s president, David Keene.