Both men campaigned Monday in Ohio, where their audiences, styles and messages produced distinctly contrasting atmospheres.
Santorum, the former Pennsylvania senator, appeared in Steubenville before a packed room including students and employees of the town's Franciscan University.
He aimed squarely at Obama as he discussed abortion, marriage, the church and family. When he touched on non-social issues such as energy and the environment, he couched them in terms of epic struggles between reasonable conservatives and radical, sometimes devious, Democrats.
"I refer to global warming as not climate science but political science," Santorum said to loud applause. He said Obama has "radical environmentalist policies" that reject robust extraction of oil and gas from many U.S. areas, including the Arctic National Wildlife Refuge in Alaska.
In Cincinnati, Romney hit Santorum's spending record as a member of Congress but stayed away from his recent comments on social and other hot-button issues.
"One of the people I'm running against, Sen. Santorum, goes to Washington and calls himself a budget hawk. Then after he's been there awhile says he's no longer a budget hawk," Romney said. "Well, I am a budget hawk."
"When Republicans go to Washington and spend like Democrats, you're going to have a lot of spending, and that's what we've seen over the last several years," Romney added.
Santorum said Obama and his allies want to frighten people about alleged dangers of petroleum-extraction techniques, including hydraulic fracturing, or "fracking," that might lower energy prices. He said those officials seek to "get your dollars, turn it to politicians who can win elections so they can control your lives."
Even with some polls showing Santorum surging, however, Romney has stuck with the same style and message he has used for months. The former Massachusetts governor sells himself as the efficient CEO who will fix the economy. He makes little mention in his standard campaign speech of the social issues that increasingly have dominated Santorum's events.
