Former president George Herbert Walker Bush will endorse Mitt Romney in Houston Thursday afternoon, the Associated Press reports:
Romney spokeswoman Gail Gitcho says the two will appear together and speak to reporters.
Formal backing from the 41st president is another sign that the Republican Party is uniting behind Romney as pressure builds on challengers Rick Santorum and Newt Gingrich to leave the race.
The elder Bush has offered encouraging words to Romney throughout the primary season but had withheld a formal endorsement. Former first lady Barbara Bush has formally backed Romney. She recorded automated telephone calls for him during the primary in Ohio.
Bush's son Jeb, the former governor of Florida, endorsed Romney last week, but former president George W. Bush has remained neutral. The elder Bush joins the other remaining GOP presidential nominees Bob Dole and John McCain in endorsing Romney.