LAS VEGAS — Republican presidential front-runner Mitt Romney engaged in a skirmish over the middle class with President Barack Obama's campaign Wednesday, a preview of a clash that could dominate a fall campaign between the two.

Fresh from a major win in Florida and heading West for a Nevada vote Saturday, Romney said he'd focus on helping the middle class, as the rich could care of themselves and the poor already had a safety net.

"I'm not concerned about the very poor," the former Massachusetts governor said on CNN from Florida on Wednesday morning before he flew off to Minnesota and then Nevada.

"We have a safety net there. If it needs repair, I'll fix it. I'm not concerned about the very rich. They're doing just fine. I'm concerned about the very heart of America, the 90-95 percent of Americans who are struggling."

But Romney's tax plan could raise taxes for lower-income families and would give big tax cuts to millionaires. Obama's campaign seized on the part about not needing to do any more to help the poor, using it to portray Romney as insensitive to the poor.

"So much for `we're all in this together,' '' Obama campaign manager Jim Messina tweeted.

"Gov. Romney hasn't proposed a single idea to help the struggling middle class or working poor," Nevada state Senate Majority Leader Steven Horsford added in a conference call arranged by the Democratic National Committee to "welcome" Romney to Nevada.

Later, in remarks aboard his campaign plane, Romney renewed his support for automatic increases in the federal minimum wage to keep pace with inflation. Business groups and most Republicans widely oppose that. Romney has held that stand since he ran for governor of Massachusetts in 2002, arguing that it would take the issue out of political debate and provide desirable stability.

The exchange came as Romney emerged as the clear front-runner for the Republican nomination after winning the Florida primary Tuesday. He and his three rivals rolled West on Wednesday, as the campaign headed into a three-week stretch in states that Romney won in 2008: caucuses Saturday in Nevada, Tuesday in Colorado and Minnesota, and Feb. 11 in Maine.

Missouri will hold a nonbinding primary Tuesday that's really just a straw poll; its delegates will be selected at caucuses in March.

Romney campaigned Wednesday in Minnesota and Nevada. Gingrich, a former speaker of the House of Representatives, campaigned in Nevada. Former Sen. Rick Santorum of Pennsylvania campaigned in and around Denver. Rep. Ron Paul of Texas campaigned in Nevada.

Romney's comments on the poor, middle class and rich served as a reminder of how much the economy dominates the political landscape in Nevada, which is not only a key site for Republican caucuses but also a likely battleground in the general election.

Unlike Gingrich, Romney didn't slam Obama for the enrollment jump in such safety net programs as food stamps, which have grown with the recession. Nor did he push any expansion of federal programs for the poor. While saying, "We can talk about whether it needs to be strengthened," he said the safety net was "very ample."

"We will hear from the Democrat party the plight of the poor," Romney said. "And there's no question it's not good being poor, and we have a safety net to help those that are very poor. But my campaign is focused on Middle Americans."

Asked what the president has done for the poor, Obama campaign spokesman Ben LaBolt said the White House had pushed through the Making Work Pay Tax Credit in 2009 and 2010, as well as a temporary payroll-tax cut in 2011. He also noted increases in spending on summer jobs for the poor, education grants for the poor and more community services for poor neighborhoods, as well as tax credits for small businesses that invest in poor neighborhoods.

Romney also said he didn't propose to help the rich.

"You can choose where to focus — you can focus on the rich — that's not my focus. You can focus on the very poor; that's not my focus. My focus is on middle income Americans, retirees living on Social Security, people who can't find work."

An analysis of his tax plan, however, shows that it could increase taxes on lower-income families and give big tax cuts to the wealthy.

Those who make less than $40,000 a year could pay higher taxes under his plan, according to an analysis by the nonpartisan Tax Policy Center. And those who earn more than $1 million would get average tax cuts of nearly $300,000.

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