President Barack Obama is calling Mitt Romney's running mate the "ideological leader" of Republicans in Congress.
He said that ideology has led to gridlock, dysfunction and a top-down approach to growing the economy.
Addressing young supporters at a Chicago fundraiser, Obama called Wisconsin Rep. Paul Ryan a decent, family man and welcomed him to the presidential race.
But Obama said he fundamentally disagrees with Ryan's vision for the country. He said Ryan and his allies in Congress mistakenly believe that fewer regulations and tax breaks for the wealthy will help create jobs.
Romney announced Saturday he had chosen Ryan as his vice presidential candidate. Democrats pounced, arguing that Ryan's budget-cutting agenda will harm seniors, students and the middle class.