COLUMBUS, Ohio—Plunging into his campaign for a new term, President Barack Obama tore into Mitt Romney on Saturday as a willing and eager “rubber stamp” for conservative Republicans in Congress and an agenda to cut taxes for the rich, reduce spending on education and Medicare and enhance power that big banks and insurers hold over consumers.

But Pres. Obama said his rival was merely doing the bidding of the conservative powerbrokers in Congress and has little understanding of the struggles of average Americans. “Why else would he want to cut his own taxes while raising them for 18 million Americans,” Pres. Obama said of his multimillionaire opponent.

The president’s campaign chose Ohio State University and Virginia Commonwealth University for the back-to-back rallies. Pres. Obama won both states in his successful race in 2008, although both have elected Republican governors since, and are expected to be hotly contested in the fall.