President Obama vowed to make climate change a priority and on Tuesday he’s giving a speech explaining how he’s going to do it. But with Congress divided on the issue of climate change, the President is expected to tackle the issue through an executive order. 

Presidents can order federal employees and agencies to enact regulations without approval from Congress, says Allan Lichtman, a history professor at American University. He says, throughout history,  presidents have used executive orders to make their mark.

“The Emancipation Proclamation by Abraham Lincoln was in effect an executive order. Harry Truman used an executive order to desegregate the armed forces,” Lichtman says.

He adds that companies and individuals can appeal to the courts, but it’s rare that they overturn executive orders. President Obama is expected to use an executive order to enact tougher regulations on power plants fueled by coal, says Kevin Book, managing director at ClearView Energy Partners. 

“You have about 2.3 billion metric tons a year of greenhouse emissions from the power sector,” he says.

That’s about a-third of the greenhouse gases produced in the United States. Book doesn’t expect the President to issue the order regulating coal plants tomorrow, but, he says, he will probably signal that one is coming soon.