President Bush has left for Britain where he will be a guest of Queen Elizabeth at Buckingham Palace. Thousands of demonstrators are expected to protest the U.S. occupation of Iraq.
It is the first official state visit for a U.S. president and security is tight in London where thousands of people are planning to demonstrate against the presence of American and British troops in Iraq.
Prime Minister Tony Blair is under increasing political pressure for joining President Bush in toppling Saddam Hussein, chiefly because their prime justification was that the Iraqi leader could help terrorists acquire weapons of mass destruction.
More than six months after Mr. Bush declared an end to major combat in Iraq, none of those weapons has yet been found.
Prime Minister Blair says this is not the time to waiver but to stand firm with the United States in fighting terrorism.
President Bush says he is not bothered by protestors and looks forward to visiting a country where people can speak freely.
The president last visited Britain in April, when he and Prime Minister Tony Blair reviewed the first weeks of the war in Iraq and progress in the Northern Ireland peace process.