United States President George Bush has praised John McCain's service and leadership in a speech to the Republican convention.
Speaking via video-link from the White House, he told delegates in St Paul, Minnesota, that Mr McCain was "a great American and the next president".
Mr McCain, 72, is due to be nominated on Thursday as the party's presidential candidate for the election on 4 November.
In his eight-minute address, Mr Bush described Mr McCain as a president ready to make the tough decisions needed "in a dangerous world".
He also spoke of Mr McCain's life as "a story of service above self" and emphasised the "independence and character" he showed in backing the administration's "surge" strategy of pouring more forces into Iraq.
Mr Bush, the toast of the 2000 and 2004 conventions who has since seen his approval ratings sink to about 30%, stayed in Washington for this one to monitor hurricane relief.
He praised Mr McCain, his rival in a bitter primary election fight eight years ago.
"He's not afraid to tell you when he disagrees. Believe me, I know," said Mr Bush, who has had an uneasy relationship with McCain over the years.
Republicans rally behind Palin
The main talking point at the convention so far has been the news that the teenage daughter of Mr McCain's running mate is pregnant.
Alaska Governor Sarah Palin was chosen as the vice-presidential nominee last week.
The disclosure that her unmarried 17-year-old daughter, Bristol, is pregnant and the news that she had hired a private lawyer in an ethics probe in Alaska have triggered a media firestorm.
Some have questioned Mr McCain's judgment in picking Ms Palin, 44, and how thoroughly the relatively unknown first-term governor's background was examined before her selection last week.
But Republicans rallied behind her at the convention on Tuesday and there was every indication that Mr McCain and other Republicans would stand by only the second woman ever picked as a major party's vice-presidential nominee.
Republicans like her anti-abortion, pro-guns stances and her history of government reform in Alaska in her two years as governor.
Mr Bush also backed the selection of Ms Palin, saying she was an "outstanding leader".
On the first night of convention speeches after a delay due to Hurricane Gustav, police used pepper spray and teargas to drive protesters away from the downtown Xcel Energy Center where the event was being held. The confrontation followed a peaceful march on behalf of poor people by more than 1,000 demonstrators.