US President George W. Bush is leading his rival John Kerry in various polls just days before the first and pivotal presidential debate on Thursday, but a second term in the White House is never guaranteed.

Bush's father lost his re-election bid in 1992 despite a post-1991 Gulf War approval rating above 90 percent. Bush says he has learned a great deal from his father's presidency and campaign and is determined to win a second term.

After receiving a Bachelor's degree at Yale University in 1968, Bush served in the Texas Air National Guard for five years while tens of thousands of people of his age, Kerry included, fought in Vietnam.

His service in the National Guard came to the forefront during the 2000 campaign and back again during this campaign. Critics accused him of favoritism, saying his father had pulled strings to help him shun the military duty in Vietnam.

But polls showed that voters this time say they would focus more on his performance at the White House than his experience more than 30 years ago.

After the guard service, Bush received an MBA from Harvard Business School in 1975. After graduating, he returned to Texas and began a career in the energy business. With a group of other investors he purchased the Texas Rangers baseball franchise in 1989 and served as general managing partner.

Bush started his first bid for office in 1978, but lost to the incumbent in a congressional race. In 1994, he returned to politics and was elected governor of Texas, a position he held for six years.

After a bitter battle of vote recounting in Florida which last more than one month, Bush was sent to the White House in the 2000 election by a 5-4 Supreme Court decision.

In the first months of office, Bush stunned the world by carrying on a series of unilateral policies. Washington refused to ratify or even withdrew from international treaties on issues such as nuclear test ban, biological weapons control, missile defense, global warming and the International Criminal Court.

The Sept. 11, 2001, terrorist attacks boosted Bush's approval rating and offered him a golden opportunity to cast himself as a strong leader and firm commander-in-chief. Bush launched a military strike in Afghanistan soon after the Sept. 11 attacks. In March 2003, he ordered a US-led invasion of Iraq despite the lack of international and UN support.

Realizing that he does not have advantage on domestic issues such as social security, health care and economy, Bush has successfully made Iraq and terrorism the center issues of this campaign. Polls have consistently showed voters giving Bush higher points over Kerry on Iraq and terrorism.

But as US casualties continue to soar in Iraq and the cost of the rebuilding continues to escalate, Bush will have to explain in the debate how the situation in Iraq will turn better only by staying the course.

Bush and first lady Laura have twin daughters.