Former Republican Senator Chuck Hagel has emerged as the leading candidate to become President Barack Obama’s next secretary of defense and may be nominated as soon as this month, according to two people familiar with the matter.

Hagel, who served as an enlisted Army infantryman in Vietnam, has passed the vetting process at the White House Counsel’s office, said one of the people. The former Nebraska senator has told associates that he is awaiting final word from the president, said the other person. Both requested anonymity to discuss personnel matters.