Gordon Brown arrives in Washington this week as the first European leader to meet with President Obama at the White House. He has pipped his closest rivals President Sarkozy and Chancellor Merkel in the race to the Oval Office, and will be only the fifth Prime Minister to be accorded the honour of addressing a joint session of Congress on Wednesday.

The visit is being spun by Downing Street as a coup for the Prime Minister, and evidence of the enduring strength of the ties between the United States and Great Britain. However, Brown's triumphal entry to the capital of the free world masks a long-term decline in the Special Relationship, which could be dramatically accelerated under the presidency of Barack Obama.

The Anglo-American alliance is being weakened on several fronts, from falling levels of UK defence spending and the gutting of Britain's armed forces by the Labour government, to the gradual erosion of British sovereignty in Europe and the rise of a European Union defence identity, now being backed by Washington. It is also threatened by apathy and indifference towards the UK on the part of the new U.S. administration, as well as by mounting American protectionism. Brown will struggle to establish a close relationship with Obama and there will be no repeat of the close-knit Bush/Blair dynamic.

President Obama's surprise decision earlier this month to remove a bust of Sir Winston Churchill from the Oval Office and return it to the British government sent an early signal to London that the Obama administration will have a far less robust approach towards the Anglo-American alliance. The White House is already recalibrating it as a "special partnership" not a "special relationship", a subtle play on words which indicates a shift away from a decades-long policy of according Britain a unique status as America's most important ally. Obama himself has seemingly little attachment to the alliance, and has never even mentioned it in a major policy speech.

Despite Brown getting his foot through the door first, there can be little doubt that the White House is keen to significantly strengthen America's relationship with both France and Germany, the biggest powers in continental Europe, as well as with Brussels, the institutional heart of the European Union. This is partly the product of a more pro-European outlook post-Bush, but is also based on a misguided belief that European allies will send more combat troops to Afghanistan, increase defence spending, and play a more supportive role alongside the United States on the world stage.

Washington is already making major concessions to France in the NATO alliance, with French officers reportedly in line to take two senior Alliance command positions. This would give Paris an extraordinary degree of power and influence within NATO, out of all proportion to its actual military role in Alliance operations, which is minimal.

The new administration is also sending clear signals that it supports a greater military and defense role for the European Union, with key appointments in both the State Department and the Pentagon being given to prominent supporters of European integration. To underscore the message, in his speech at the Munich Security Conference, Vice President Joe Biden made it clear that the United States will "support the further strengthening of European defense, an increased role for the European Union in preserving peace and security, (and) a fundamentally stronger NATO-EU partnership."

It would be a huge mistake for the new U.S. administration to look away from Britain for its most important strategic partnership. There has scarcely been a more important period since the Second World War for joint U.S.-British leadership, with a major war in Afghanistan, a global battle against al-Qaeda, an increasingly aggressive Russia, and the prospect of a nuclear-armed Iran.

There is no evidence to suggest that Europe is capable of shouldering the burden of global leadership with America. The European Union is a grandiose emperor with no clothes, and its track record in confronting dictatorial regimes such as Iran has been a dismal failure. The EU is obsessed with challenging American global pre-eminence rather than working with the United States, and the European Project is ultimately all about building a counter-weight to American world leadership.

The Special Relationship is vital to American and British interests on many levels, from military, diplomatic, and intelligence cooperation to transatlantic trading ties. If President Obama does not invest in its preservation, the end result will be a weaker United States that is less able to stand up to terrorism and tyranny, and project power and influence across the globe.

Former Secretary of State Henry Kissinger famously spoke of Washington needing a single telephone number to call in Europe in a crisis. In practice that number has for decades been in London, and if President Obama decides to switch it to Brussels or another European capital the world will be a far more dangerous place.

Great Britain is America's most reliable friend. Whether waging war against the Taliban and al-Qaeda, standing up to the Russian bear, or halting Iran's nuclear ambitions, President Obama should maintain the Anglo-American Special Relationship as the centerpiece of the transatlantic alliance. As nearly every post-war president has found, there is simply no alternative to U.S.-British leadership in securing the free world.

Nile Gardiner is Director of the Margaret Thatcher Centre for Freedom at the Heritage Foundation in Washington, DC.