Trump had refused to rule out a third-party run during the Aug. 6 Republican debate.
NEW YORK -- Donald Trump will sign a pledge to back the Republican presidential nominee and not to run as an independent should he not win the party's nomination, multiple outlets have reported.
20:19 How Steve Bannon Lost the Battle for the Soul of Trumpism33
14:02 Steve Bannon: 'No administration in history has been so divided'40
04:14 Stephen Bannon: 'No administration in history has been so divided'37
04:12 Trump will not pardon Sheriff Joe Arpaio 'today,' White House says19