Monday, February 20th 2012, 5:27 PM EST
Rick Santorum told supporters that President Obama was "imposing his ideology" on US policy
US Republican presidential hopeful Rick Santorum has renewed an attack on President Barack Obama's environmental policy, calling it "political science'.
Mr Obama unwisely limits energy production, he said, saying science supported backers of oil exploration.
Mr Santorum spoke after drawing criticism at the weekend for saying Mr Obama supported a "phony theology".
The former Pennsylvania senator has seen his support rise since winning three state contests two weeks ago.
He faces a key test next week in primary elections in Arizona and Michigan on 28 February.
Long-time front-runner Mitt Romney hails from Michigan, where his father served as governor, but he currently trails Mr Santorum in polling there.
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Correspondents say defeat for Mr Romney in what is effectively his home state would sow panic in the Republican establishment and increase the chances of a messy, drawn-out end to the nomination process.
After Michigan several states, including key presidential battleground Ohio, will hold contests on "Super Tuesday", on 6 March.
The eventually Republican nominee will face President Barack Obama in November's general election.
Speaking on Monday at a campaign stop in Ohio, Mr Santorum hit out at the concept of global warming, and said that as president he would support the coal industry.
"I refer to global warming as not climate science, but political science," he said.
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