President Barack Obama's senior campaign adviser David Axelrod says the Medicare changes supported by Rep. Paul Ryan, the likely Republican vice presidential candidate, would put the popular health-care plan for the elderly in "a death spiral."

Axelrod said on CNN's "State of the Union" on Sunday that Obama thinks Ryan is a friendly and intelligent man, but he disagrees with his ideas on the direction of government. Axelrod described Ryan as "a right wing ideologue" who wants to convert Medicare into a voucher plan. Axelrod said the president believes that Medicare needs to be strengthened but considers Ryan's plans "a Trojan horse" that would eventually lead to the program's demise.

Likely GOP presidential nominee Mitt Romney announced on Saturday that the 42-year-old Wisconsin congressman would be his running mate.