US President Barack Obama is making good on his pledge to politicise gun violence.

The package of gun-control executive actions Obama will formally announce on Tuesday has pushed the contentious issue to the forefront of the 2016 presidential campaign.

Public opinion polls show that Americans overwhelmingly support expanding background checks for gun purchases but are more divided on the broader question of stricter gun laws.

Although Obama cannot unilaterally change gun legislation, he is hoping that beefing up enforcement of existing laws can prevent at least some gun deaths in a country that has witnessed more than 100,000 killings over the past 10 years.

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"This is not going to solve every violent crime in this country, it's not going to prevent every mass shooting, it's not going to keep every gun out of the hands of a criminal - but it will potentially save lives in this country," Obama said on Monday. 

The gun-control advocacy movement has gained wealthy backers, including the former New York City Mayor Michael Bloomberg, but the National Rifle Association, which supports gun owners' rights, remains one of the most dominant forces in American politics.

Republican contenders promise that if they get elected, they will swiftly repeal Obama's actions, which include steps to expand background checks for gun purchases.

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Republican frontrunner Donald Trump vowed to "unsign" the president's measures. Florida Senator Marco Rubio said that on his first day in the White House, "those orders are gone". Texas Senator Ted Cruz said that while Obama may currently hold the power of the pen, "my pen has got an eraser".

On the Democratic side, frontrunner Hillary Clinton has unveiled her own proposals for gun-control executive actions. At a rally in Iowa, she enthusiastically endorsed Obama's measures. "I won't wipe it away," Clinton said.

The emphasis on gun issues marks a shift for Democrats, who have shied away from the subject in recent presidential elections, not only because of the NRA, but because of competing views within the party.

Actions to expand background checks have broad public support. A CBS/New York Times poll conducted in October found that more than 90 percent of Americans favour requiring background checks on all potential gun buyers.

"There's more organisation, there's more capacity, there's more money," said Kristin Goss, a public policy professor at Duke University who has studied gun-control pressure groups. But asked whether new organisations can succeed in matching the energy and organisational power of the NRA in a general election, Goss said:  "That's an open question."

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Source: Associated Press