IOWA, USA (AFP) — President Barack Obama took aim at his Republican rival’s newly announced running mate yesterday, accusing Paul Ryan of blocking help for farmers during a swing through drought-stricken Iowa.

Obama launched a three-day campaign bus tour of a key swing state that nurtured his White House dream four years ago, as Ryan — Mitt Romney’s pick for vice-president — tried to spoil the president’s political homecoming.

But Ryan swiped back as his own coming out party also hit Iowa, the kind of midwestern battleground where the Romney campaign hopes the number crunching Wisconsin congressman will swell Republican turnout on November 6.

The president, joining his campaign’s bid to define Ryan negatively for voters, said the Republican number two thwarted efforts in Congress to pass a bill to aid farmers suffering one of the worst droughts in 50 years.

“If you happen to see Congressman Ryan, tell him how important this farm bill is to Iowa and our rural communities,” Obama told a crowd in Council Bluffs near the Nebraska border, the first stop for his sleek armoured bus.

Tying Ryan to the unpopular US legislature, Obama slammed the Republican vice-presidential nominee as “the ideological leader of the Republicans in Congress”.

“I know Congressman Ryan. He’s a good man, he’s a family man,” Obama said. “He is an articulate spokesman for Governor Romney’s vision, but the problem is that vision is one that I fundamentally disagree with.”

Earlier the White House announced the government would buy up US$170 million of excess pork, lamb and catfish to support farmers, and the Pentagon will examine whether it can buy extra food stocks to freeze and use later.

The move was an indication of the way an incumbent president can use his power to appeal to wavering voters as he seeks re-election.

Obama also halted his motorcade at a family farm, and spoke of the need to pass the farm bill against a backdrop of parched corn stalks baked brown by a lack of water.

In an example of the maxim that all politics is local, Obama also hammered Romney on his opposition to the extension of a wind energy tax credit designed to encourage green technology which is due to expire at the end of the year.

He said that Romney’s position could put wind energy at risk in Iowa and cost 7,000 jobs in the state, along with 37,000 countrywide.

Ryan hit back at the Iowa state fair, a rite of passage for presidential candidates which for years featured life-size butter cow sculptures by a woman named Norma Lyon, who endorsed Obama in 2007 and died in May.

Ryan was heckled as he spoke, but he shrugged off the interruption to lambast Obama as a big spending liberal.

“President Obama has given us four years of trillion dollar plus deficits. He’s spending our children into a diminished future,” Ryan said.

Romney meanwhile headed south to Florida into a row over Medicare, the state health program for seniors which Democrats say would be gutted under a budget proposal advanced by Ryan in the House of Representatives.

The Republican challenger accused Obama of spending $700 million to pay for his health care reform law, which conservatives revile, and like Ryan pledged to restore US fiscal health.

“We want to get America on track to a balanced budget … we simply can’t afford ObamaCare,” Romney said.

Ryan has rejected criticism of his approach to Medicare, arguing his reforms are needed to save the program from bankruptcy rather than to destroy it.

Romney and Ryan back across the board tax cuts and reductions in government spending, but Democrats say the middle class would foot the bill and only the wealthy would benefit.

The Obama campaign also thinks elderly voters in states like Florida, and the white working class voters elsewhere with whom Obama has trouble connecting, could be spooked by Romney and Ryan’s plans for social programmes.

Iowa has a special place in Obama’s heart as it is where he built the foundation of the grass roots movement that upset Hillary Clinton’s political machine on the way to the Democratic nomination in 2008.

But four years on, his promises of hope and change have been tarnished by the painful choices of governing in a bitterly divided political environment and the worst financial crisis in 70 years.

Recent polls in Iowa show the race essentially tied, though the volume of polling has been fairly sparse so it is tough to judge who is in the lead.

In Florida, Romney praised US victories in the Olympics and the space race, but in front of crowds that appeared smaller and more subdued than those he drew with his new running mate.

A Fox News national poll out Thursday put Obama at 49 per cent to Romney’s 40 per cent, while a CNN poll had Obama at 52 per cent, seven points up on the former Massachusetts governor.

But a Democracy Corps poll Monday had the race essentially tied.