COUNCIL BLUFFS, Iowa  - President Barack Obama took aim at his Republican rival’s newly-announced running mate Monday, accusing Paul Ryan of blocking a farm bill during a swing through drought-stricken Iowa.

Obama launched a three-day campaign bus tour of Iowa, 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.

Obama drew a sharp contrast between his positions on the economy and taxes and those of Romney, his Republican challenger, whose campaign has gained energy since he named Ryan as his running mate on Saturday.

The president said Ryan was thwarting efforts in Congress to pass a bill to aid farmers and ranchers suffering one of the worst droughts in 50 years and sought to exploit the rock-bottom approval ratings of the US legislature.

“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 armored bus.

He slammed Ryan as “the ideological leader of the Republicans in Congress,” blaming him for the political gridlock in Washington, which has infuriated many Americans in search of relief during a sluggish economic recovery.

“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 that it would buy up $170 million of excess pork, lamb, catfish and chicken 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 voters in key states as he seeks re-election.

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.

In Florida on Monday 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 percent to Romney’s 40 percent, while a CNN poll had Obama at 52 percent, seven points up on the former Massachusetts governor.