WASHINGTON » Mitt Romney struggled to steady his presidential campaign today, buffeted by an outbreak of sniping by frustrated Republicans, fresh evidence of a slide in battleground state polls and President Barack Obama’s accusation that he was writing off "half the country" in pursuit of the White House.

Republican running mate Paul Ryan drew boos at an AARP convention in New Orleans when he said Romney would repeal Obama’s health care law, which closed a gap in coverage for seniors’ prescription drugs. The Wisconsin congressman accused the administration of weakening Medicare and flinching from tough measures needed to stabilize Social Security’s finances, adding that the president has "put his own job security over your retirement security."

Obama rebutted Ryan’s charges point by point in a video appearance to the same audience. He said the Republican prescription for Medicare would mean "billions in new profits for insurance companies" and replacing guaranteed benefits with a voucher that would bring higher out of pocket costs for seniors.

Romney campaigned in Nevada as aides released a 2011 federal income tax return showing he and his wife, Ann, paid $1.94 million in federal taxes last year on income of $13.7 million. Their effective tax rate was 14.1 per cent, lower than many families pay because most of the couple’s earnings come from investments.

The campaign also released a letter from Romney’s doctor saying the 65-year-old former Massachusetts governor is healthy and physically up to the demands of the presidency.

Republicans tried to yank the campaign focus back to the economy.

"While President Obama and Democrats will try to distract voters, Mitt Romney and Paul Ryan are focused on fixing the economy, getting Americans back to work and ensuring a better future for our children and grandchildren," Sen. John McCain, the Republicans’ 2008 presidential candidate, said in a statement.

But there seemed no letup in the bad political news for Romney, hit by a barrage of it since he was seen on videotape saying that his job as a candidate is not to worry about the 47 percent of Americans whom he said pay no income taxes and see themselves as victims.

Obama, for sure, was eager to keep the controversy alive. Campaigning in Woodbridge, Va., he defended himself against Romney’s jabs in response to his own statement that change is impossible from the inside in Washington. "It can’t happen if you write off half the nation before you even took office," he said.

According to Wall Street Journal/NBC News/Marist Poll surveys, the president has opened leads among likely voters of eight percentage points in Iowa, with 6 electoral votes, and margins of five percentage points each in Colorado (9 electoral votes) and Wisconsin (10.)

Earlier surveys published this week pointed to leads for Obama in both Virginia, with 13 electoral votes, and Ohio, with 18.

National polls have been far closer, including an AP-GfK survey this week that had it a statistical tie among likely voters. They have also suggested progress for Obama in terms of his handling of the economy, the No. 1 issue in the race.

Despite Romney’s difficulties, recent soundings on employment have not been encouraging for the president’s re-election. Newly released figures show joblessness ticked up in five swing states in August, fell in two and was unchanged in two others.

Romney’s allies also point to a series of presidential debates beginning Oct. 3 as a chance to shake up the race.

But for now, Romney’s troubles have sent shudders down ballot, where Republicans are in tough races that will settle the outcome for the struggle for control of the Senate this fall. Tommy Thompson, dropping in the polls in Wisconsin, said "the presidential thing is bound to have an impact on every election."

That produced a quick retort from John Sununu, a top Romney surrogate. "My good friend Tommy Thompson sounds like Barack Obama, blaming it on somebody else," he said on CNN.

But Thompson wasn’t alone. Rep. Rick Berg, running for the Senate in a closer-than-expected race in North Dakota, became the latest in a string of Republican candidates to say they disagreed with Romney’s 47 percent remarks.

Apart from his self-inflicted political wounds, Romney has been under pressure from fellow Republicans to draw clearer distinctions with Obama on the economy, and say more clearly what he would do to bring down the nation’s 8.1 percent unemployment rate.

Asked to point to new policy proposals that Romney has made since early August, aides referred to one speech on energy independence and a set of remarks on veterans.

But he has generally been unwilling to flesh out his plans for balancing the budget or enacting tax reform, refusing, for example, to name a tax break he would eliminate except for a small one that subsidizes producers of wind power.

He criticized Obama’s handling of anti-American demonstrations around U.S. embassies in the Middle East earlier in the month, but declined to say what approach he would have taken instead. And while he has repeatedly tagged Obama for not being more forceful in trying to arrange the downfall of Syrian President Bashar Assad, aides have refused for nearly a month to say whether the Republican challenger supports arming rebels fighting the regime.

Ryan provided no new policy details in his appearance before the AARP, although he renewed Romney’s support for a gradual increase in the Social Security retirement age and slowing the growth of benefits for those at higher incomes. Republicans have yet to provide details.

He told seniors that Republicans "respect you enough to level with you," and said Obama’s health care legislation had cut $716 billion out of Medicare over a decade and set up a board of unelected bureaucrats with authority to make future reductions so severe they could eventually jeopardize seniors’ access to medical care.

"You know President Obama’s slogan, right? Forward." he said, then added, mockingly, "Forward into a future where seniors are denied the care they earned because a bureaucrat decided it wasn’t worth the money."

Obama answered via video hookup and a television commercial that began airing in Florida, Colorado and Iowa. It argued that under the Republican plan, seniors’ health costs could go up by $6,400 a year.

Obama has said he would consider raising payroll taxes on upper-income wage earners to shore up the trust fund that pays for Social Security benefits. Workers currently pay a 4.2 percent tax on income up to $110,100 annually, although the rate is scheduled to revert to a previous 6.2 percent at the first of the year.

Associated Press writers Mark Smith in Woodbridge, Va.; and Ken Thomas, Jim Kuhnhenn, Julie Pace and Kasie Hunt in Washington contributed to this report.