By RICK M. GREEN Capitol Bureau rmgreen@oklahoman.comGov. Mary Fallin, who has withheld her endorsement of any candidate in the Republican presidential race, threw her support behind Donald Trump on Wednesday. In brief comments to reporters after a public event, she said she stands behind the New York billionaire, who favors building a huge wall along the nation's southern border and making Mexico pay for it. Fallin, who has represented Oklahoma in the U.S.