Mitt Romney all but secured the Republican nomination after Rick Santorum suspended a tenacious shoestring campaign, paring down the US presidential race to two clear choices.

A charismatic Democratic president, vulnerable to any sign that the tentative economic upswing might stall, faces off against a multimillionaire who has struggled to connect with his own party's conservatives but hopes his business background will convince voters he can put the country on a path to sturdier recovery.

Now Romney and President Barack Obama are free to focus on confronting each other, something they had already been increasingly doing in recent weeks as the former Massachusetts governor gradually emerged as his party's likely nominee.

Neither has hesitated to draw sharp contrasts with the other.

Obama, whose re-election prospects have been buoyed by the divisive state-by-state Republican primary race, said the choice facing voters this November was one of the starkest in recent history.

Traveling to Florida, Obama opened a new push to revamp the US tax law under which wealthy investors often pay taxes at a lower rate than middle-class wage-earner. The proposal stands little chance of passing in Congress but serves as a clear general election contrast with Romney.

"We've got to choose which direction we want this country to go," Obama told a boisterous audience of students at Florida Atlantic University.

"Do we want to keep giving tax breaks to folks like me who don't need them?" he added, referring to his own personal wealth, estimated at between $1.8 million and nearly $12 million.

Obama said Democrats would ensure the rich pay their fair share, while focusing on investments in education, science and research and caring for the most vulnerable. By contrast, he said, Republicans would dismantle education and clean energy programs so they can give still more tax breaks to the rich.

Obama did not mention Romney by name, but the economic fairness message was the theme of his day - and aimed squarely at the former governor, who once headed a private equity firm and is worth up to $250 million.

The renewed focus on the economy suits Romney, whose conservative credentials are suspect among the Republican base because of his past moderate stances on social issues such as abortion - polarizing topics that were pushed to the forefront by Santorum's presence.

Santorum's 3-year-old daughter has been released from a Virginia hospital and is settling in at home with her parents, a campaign spokesman said on Tuesday.

Bella Santorum, who suffers from a rare genetic condition called Trisomy 18, was hospitalized on Friday as her father began a brief holiday break from campaigning. Santorum carries a photo of Bella and often says she wasn't expected to live beyond her first birthday. Her story is well-known to religious conservatives who back Santorum because of his strong position against abortion.

Mitt Romney all but secured the Republican nomination after Rick Santorum suspended a tenacious shoestring campaign, paring down the US presidential race to two clear choices.

A charismatic Democratic president, vulnerable to any sign that the tentative economic upswing might stall, faces off against a multimillionaire who has struggled to connect with his own party's conservatives but hopes his business background will convince voters he can put the country on a path to sturdier recovery.

Now Romney and President Barack Obama are free to focus on confronting each other, something they had already been increasingly doing in recent weeks as the former Massachusetts governor gradually emerged as his party's likely nominee.

Neither has hesitated to draw sharp contrasts with the other.

Obama, whose re-election prospects have been buoyed by the divisive state-by-state Republican primary race, said the choice facing voters this November was one of the starkest in recent history.

Traveling to Florida, Obama opened a new push to revamp the US tax law under which wealthy investors often pay taxes at a lower rate than middle-class wage-earner. The proposal stands little chance of passing in Congress but serves as a clear general election contrast with Romney.

"We've got to choose which direction we want this country to go," Obama told a boisterous audience of students at Florida Atlantic University.

"Do we want to keep giving tax breaks to folks like me who don't need them?" he added, referring to his own personal wealth, estimated at between $1.8 million and nearly $12 million.

Obama said Democrats would ensure the rich pay their fair share, while focusing on investments in education, science and research and caring for the most vulnerable. By contrast, he said, Republicans would dismantle education and clean energy programs so they can give still more tax breaks to the rich.

Obama did not mention Romney by name, but the economic fairness message was the theme of his day - and aimed squarely at the former governor, who once headed a private equity firm and is worth up to $250 million.

The renewed focus on the economy suits Romney, whose conservative credentials are suspect among the Republican base because of his past moderate stances on social issues such as abortion - polarizing topics that were pushed to the forefront by Santorum's presence.

Santorum's 3-year-old daughter has been released from a Virginia hospital and is settling in at home with her parents, a campaign spokesman said on Tuesday.

Bella Santorum, who suffers from a rare genetic condition called Trisomy 18, was hospitalized on Friday as her father began a brief holiday break from campaigning. Santorum carries a photo of Bella and often says she wasn't expected to live beyond her first birthday. Her story is well-known to religious conservatives who back Santorum because of his strong position against abortion.