Washington - One of John McCain's biggest challenges between now and November's general election will be exactly how to use his Republican compatriot George W Bush - an unpopular two-term president who still appeals to the party's conservative base.

President Bush and Vice President Dick Cheney are scheduled to speak Monday night at the Republican Party's nominating convention in St Paul, Minnesota.

It will be one of only a few high-profile appearances Bush has made since March in support of McCain, who will formally accept the party's nod to run for the White House on Thursday.

Bush's approval rating has hovered under 30 per cent for many months, as the United States economy flirts with a recession, while US troops remain engaged in an unpopular war in Iraq and face a Taliban resurgence in Afghanistan.

It was a favourite refrain of the Democrats at their own convention to compare a McCain administration to a "third Bush term," linking McCain to the current president on everything from tax policy to his support for the 2003 invasion of Iraq.

"The record's clear: John McCain has voted with George Bush 90 per cent of the time," Barack Obama said in accepting the Democratic Party's presidential nomination three days ago. "I don't know about you, but I'm not ready to take a 10-per-cent chance on change."

For his part, McCain has spent much of the campaign bolstering his own longstanding image as an anti-establishment maverick who is not afraid to take on Bush and his own party. This summer he ran a television advertisement that flatly said the country was "worse off than we were four years ago."

Many observers believe the general election will depend on which side wins this argument - whether McCain provides enough change from Bush that voters will be prepared to elect another Republican to office.

The McCain-Bush relationship has been strained ever since a bruising 2000 Republican primary election.

During Bush's time in office, McCain has supported tougher US action on global warming, opposed torture and strongly criticized the post-war management of Iraq. He demanded the resignation of former defence secretary Donald Rumsfeld.

On the other side, McCain has promised to extend Bush's 2001 tax cuts, which heavily favour wealthier Americans and which he opposed at the time. McCain has also called for victory at all costs in Iraq and is a strong supporter of free trade.

While McCain has said he would be "privileged" to have Bush play a role in the campaign, it is unclear just how often voters will see Bush and McCain on the trail together between now and November.

In a ringing endorsement in March, Bush said McCain would "bring determination to defeat the enemy," but the president also seemed to recognize the pitfalls of too close an association.

"If (McCain) wants me to show up, I will. If he wants me to say I'm not for him, I will," Bush quipped in a joint appearance at the White House.

But Bush does bring strengths to the table, particularly on the crucial issue of fundraising. He still appeals to Republican donors, and a plea for cash is something which he has already made at a few closed-door events in support of McCain.

For the first time in modern history, Democrats have been out- raising Republicans in this election cycle. Obama has received a record 389 million dollars in donations to date, compared to McCain's 159 million dollars.

Bush was the most prolific fundraiser until Obama came along, and his pull with conservatives is still likely to boost McCain's own level of donations. (dpa)