ATLANTA - The South is where President Barack Obama and Democrats long have struggled, and it's where the party's toughest battleground will be this year in the fight for control of the U.S. Senate.

Three incumbents must face the consequences of having voted for Obama's health care law, but Republicans first must settle primaries in several states, including a challenge to Minority Leader Mitch McConnell of Kentucky.

All but one of the potentially competitive races is in a state Obama lost in 2012, and the president remains deeply unpopular among whites in the region. Republicans are optimistic they can achieve the six-seat gain needed to retake the Senate.

Democratic Sens. Kay Hagan of North Carolina, Mary Landrieu of Louisiana and Mark Pryor of Arkansas are on the ballot for the first time since voting for the Affordable Care Act in 2010. The law's wobbly start and its image as a power-grab have the incumbents on the defensive, emphasizing local issues and avoiding unnecessary mention of the second-term president who leads their party.

Obama's Gallup job approval lingers in the low 40s, and is even lower in several states with pivotal Senate races. Republicans want to feed on that and follow the same road map that carried them to a House majority in 2010, Obama's first midterm election.

"Democrats hope this doesn't become a national election, but we don't think that's the case," said Republican National Committee spokesman Michael Short.

Democrats want the Republican primaries to project divisions and extremism. With Congress more unpopular than the president, they seek to highlight those Republican Senate candidates who are already serving in the House.

In 2012, Democrats defied early predictions and expanded their Senate majority by winning in GOP-leaning Missouri and Indiana, where conservative candidates tripped over their own pronouncements on rape and other issues.

A look at Senate races across the South:

-Arkansas sets up as a proxy for the tussle between the White House and House Republicans. Pryor, whose father served as governor and U.S. senator, is the last remaining Democrat in the state's Capitol Hill delegation. His Republican opponent, U.S. Rep. Tom Cotton, is a young conservative favorite.

Cotton and Pryor avoided primaries. Cotton voted with GOP leaders in October to end the partial federal government shutdown, but Democrats say they can paint him as extreme. They're already pointing to his vote against the new farm bill.

Arkansas voters, who give Obama a 35 percent approval rating, have seen a barrage of ads reminding them that Pryor was "the last vote" on the health care bill.

-In Georgia, where Republican Sen. Saxby Chambliss is retiring, a May primary is almost certain to lead to a runoff.

Three congressmen - Jack Kingston and doctors Phil Gingrey and Paul Broun - each says his record proves his conservative bona fides.

Kingston, chairman of a House Appropriations subcommittee, tells voters what he's cut in the federal budget.

Gingrey's slogan is "Repeal or go home," and he's banking on his opposition to the president's health law carrying the day.

Broun, who once declared evolutionary theory "lies straight from the pit of hell," says his colleagues are poseurs. He tried to prove his conservative credentials by holding a drawing for an AR-15 military style rifle.

Karen Handel, a former secretary of state and commission chairman in Georgia's most populous county, says she's got the right experience for the job, and without the blemish of serving in Congress.

Former Dollar General and Reebok CEO David Perdue, the cousin of former Gov. Sonny Perdue, says business experience should trump the lot of "career politicians," and he's said he's willing to finance his own race.

The Democratic favorite is Michelle Nunn, the daughter for former U.S. Sen. Sam Nunn. Democrats are confident that she can pull in just enough Mitt Romney voters - rural and small-town whites fond of her father, and suburban white women in metropolitan Atlanta - for an upset.

-In Kentucky, McConnell finds himself criticized from the left and right. Wealthy businessman Matt Bevin may be a long shot in the Republican primary, but he's got enough organization and money to grab attention as he brands McConnell a capitulator to Obama.

Democrats back Secretary of State Alison Lundergan Grimes, a party financier's daughter who has gotten campaign advice and help from former President Bill Clinton. Like Nunn in Georgia, Grimes wants to win big among women. Like Bevin, she is going after McConnell as part of the problem in Washington, but she also says McConnell cares more about his national party post than about Kentucky.

McConnell has plenty of money to respond. He'd already spent $10 million by the end of 2013.

-In Louisiana, Landrieu is seeking a fourth term never having topped 52.1 percent of the vote. She won twice in Democratic presidential years. She won in 2002, a midterm year, by running as a centrist who could work with a Republican White House. This time, she has to run with Obama's negatives - a 40 percent approval rating in Louisiana, according to Gallup - without having him at the top of the ticket to excite Democrats, particularly black voters.

U.S. Rep. Bill Cassidy has the backing of national Republican leaders and donors. But he once contributed to Landrieu and, as a state senator, he pushed a proposal similar to Obama's health insurance exchanges. At least two other Republicans will be on the all-party primary ballot. Unless one primary candidate receives more than 50 percent of the vote, the top two candidates go to a runoff in December. That second round of voting might be Cassidy's best shot at winning the Senate seat.

Landrieu defends her health care vote but has clamored for changes to the law. Democrats cite her influence as head of the Senate Energy and Natural Resources Committee, saying her post is a boon for Louisiana's oil-and-gas industry and hammering Cassidy as a rubber stamp for House Republicans. Both she and Cassidy champion flood insurance relief for coastal residents.

-Mississippi hasn't seen Sen. Thad Cochran truly campaign in decades. That's changing with a challenge from state Sen. Chris McDaniel, who boasts endorsements from national conservative and tea party groups. Cochran backers answered with a super political action committee organized by Henry Barbour, the nephew of the former RNC chairman and Gov. Haley Barbour.

McDaniel wants to turn Cochran's greatest asset - his experience and what it's meant financially to Mississippi - into a liability by making the incumbent the face of the nation's $17 trillion debt. The Cochran team attacks McDaniel's legislative votes supporting bond debt for public projects. The comparison, McDaniel says, is intellectually dishonest. Henry Barbour counters that McDaniel casting Cochran as a "big-government liberal" is just as ludicrous.