Sen. John McCain will officially receive the endorsement of President George W. Bush today at the White House:

UPDATE: The endorsement is expected at 1:00 PM ET.

Republican presidential nominee-in-waiting John McCain has a lunch date Wednesday with President Bush at the White House - and the promise of a Bush endorsement.

There'll be a formal welcome at the North Portico, followed by lunch in Bush's private dining room and an endorsement in the Rose Garden.

In recent weeks, Bush has gone out of his way to defend the senator's conservative credentials, saying criticism on McCain has been grossly unfair. The two were bitter rivals in 2000.

``The president has said he looks forward to vigorously campaigning for the GOP and tonight it has become clear that the GOP nominee will be Sen. John McCain,'' White House press secretary Dana Perino said Tuesday night. ``Of course the president is going to endorse the GOP nominee, which is going to be Senator John McCain.''