JEFFERSON CITY, Missouri (AP) — Mitt Romney will headline the annual convention of the most powerful American gun lobby on Friday, courting gun-rights activists even as the fatal shooting of an unarmed black teenager thrust the divisive issue of arms control to the forefront of election-year politics.

The Republican presidential candidate’s efforts to assure the National Rifle Association that he is on its side — despite having once spoken dismissively of the group — is a reflection of how deeply many U.S. voters believe in their constitutional right to bear arms.

Even President Barack Obama has virtually ignored gun issues during his term despite promises to develop steps on weapons safety. The NRA nonetheless considers Obama a foe and plans to mount an aggressive effort against him.

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The right to bear arms is guaranteed by the U.S. Constitution, although the country is fiercely divided over how exactly to interpret the Second Amendment that protects gun possession. The uproar over the shooting of 17-year-old Trayvon Martin at the hands of a volunteer neighborhood watchman in Florida has galvanized pro- and anti-gun control activists alike.

The NRA convention in St. Louis, Missouri, provides Romney an opportunity to shore up his credentials with conservatives who have not always trusted his reliability on social issues — including gun control. Running for the Senate in Massachusetts decades ago, Romney once assured voters in a state with strong gun-control laws: “I don’t line up with the NRA.”

It won’t be the first time Romney has had to walk a careful line between appealing to conservatives, who form his party’s base, and trying not to alarm independents, who will be crucial in his campaign against Obama.

Romney will speak to a conservative group with one of the biggest names and broadest networks in U.S. politics. Thousands of members are filling St. Louis hotels and sidewalks this weekend for an annual convention that offers “over seven acres of guns, gear and outfitters.”

The all-but-certain Republican presidential nominee hopes to tap into the NRA’s network more than 4 million dues-paying members. Romney virtually secured his party’s nomination this week when his main rival, Rick Santorum, dropped out of the state-by-state Republican primary race.

The NRA has spent $20 million to $30 million in past presidential elections, said NRA spokesman Andrew Arulanandam. It hopes to exceed that amount this year in an effort that is likely to include mail, phone calls and TV, radio, Internet and newspaper ads, he said.

Romney leads a list of prominent Republicans who are scheduled to address more than 65,000 convention registrants during a session billed as a “celebration of American values.”

While some gun-control advocates might be turned off by Romney’s association with the NRA, there’s little likelihood such activists were going to vote for him anyway, leaving little political downside for Romney’s appeals to NRA faithful, said Dave Robertson, a political science professor at the University of Missouri-St. Louis.

Yet Romney’s alignment with the NRA comes at a time when gun laws have been under national scrutiny.

The NRA was a main backer of Florida’s “stand your ground” law, which bolstered gun owners’ rights to use deadly force rather than retreat from danger.

That self-defense law has been much discussed in relation to Martin’s death in February. After authorities initially declined to charge him, neighborhood watchman George Zimmerman was charged Wednesday with second-degree murder. Zimmerman’s attorney has said the defendant will plead not guilty and invoke the “stand your ground” law.

Romney has said little about whether he favors such laws, though he has called the shooting a “terrible tragedy” and has said it was appropriate for prosecutors to look into the case.

After the shooting, Obama said, “If I had a son, he’d look like Trayvon.” And while he said at the time that he supported the investigation, he didn’t address the issue of guns.

In fact, Obama has hardly talked about the issue since a couple of months after the January 2011 assassination attempt on Congresswoman Gabrielle Giffords in Tucson, Arizona, when the president promised to develop new steps on gun safety.

Romney hasn’t always been in the NRA’s good graces.

As a challenger to Democratic Senator Edward Kennedy in 1994, Romney professed not to line up with the group. When he was running for Massachusetts governor in 2002, the NRA shied away from making any endorsement and gave Romney’s Democratic opponent a better rating on gun-rights issues.

Massachusetts quadrupled its gun-licensing fee while Romney was governor. He also signed a 2004 law that made permanent a ban on assault-type weapons, though it was coupled with measures backed by gun-rights groups, such as a lengthening of the firearm license period from four to six years and the creation of an appeals board for people seeking to restore their gun licenses.

As he was considering his first presidential run in 2006, Romney signed up for a lifetime membership in the National Rifle Association.

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Associated Press writer David A. Lieb contributed to this report.

Copyright 2012 The Associated Press.