Could to pull out

"The U.S.-South Korea free-trade agreement, known as KORUS, allows the United States to terminate it after six months if it wishes to. So if Trump signed a letter to withdraw from the agreement, the deal would effectively be terminated in March 2018. KORUS was approved by Congress, but Trump could to pull out of the agreement on his own." (The Washington Post.)

Why does the infinitive "to pull out" follow the modal "could" in the passage above?