WATCH: In opening salvo, Obama calls Ryan 'ideological leader'
Remarks are U.S. president's first comments about Republican challenger Romney's selection of the Wisconsin congressman as his running mate.
U.S. President Barack Obama on Sunday dubbed Paul Ryan as the "ideological leader" of congressional Republicans, in an opening salvo against Mitt Romney's vice presidential running mate, who Democrats are painting as a budget hawk and defender of the rich.
"Just yesterday, my opponent chose his running mate, the ideological leader of Republicans in Congress, Mr Paul Ryan. I want to congratulate Mr Ryan. I know him, I welcome him to the race," Obama said at a fundraiser in Chicago, speaking over boos from some in the audience at the mention of Ryan's name.
"He's a decent man. He is a family man. He is an articulate spokesman for Governor Romney's vision. But it's a vision that I fundamentally disagree with," he said.
The remarks were Obama's first comments about Republican challenger Romney's selection of the Wisconsin congressman as his running mate, which has injected new energy into the Republican presidential campaign.
But Obama and his fellow Democrats are keen to attack Ryan for his controversial budget plan, which they say would dismantle popular social programs that help the elderly and the poor.
Obama mentioned Ryan after complaining about the "top down" economics of Republicans in Washington.
"This kind of top down economics is central to Governor Romney and it is central to his running mate," he said.