AS OUR SMALL aircraft rolled and pitched in the sky above Houston, Texas, in early 1999, William Hague showed me the list of questions that he was planning to put to the Governor of Texas, George W. Bush, and asked me if I had anything to add.

“Texas has one of the highest prison populations in the United States,” I said. “Governor Bush is uncompromising about capital punishment, promotes education vouchers, is tough on welfare cheats and wears alligator-skin boots that go halfway to his knees with the word ‘Governor’ embossed on them. And yet everyone calls him a compassionate conservative. You might ask him how he does it.”

A couple of hours later, sitting in the Governor’s office, George Bush gave us his answer. “It’s because I try,” he said. And he explained how he was reaching new audiences among immigrants and the poor and using a new rhetoric that appealed to the social conscience of the middle class.

He could equally well have given this answer: “It’s because of Karl Rove.” For 30 years Rove has been George Bush’s friend, and for the past ten he has been constantly at his side, plotting his rise, mapping out his campaigns, devising his agenda. It is Rove who first became convinced that if conservatives wanted to win power and keep it, they needed to change, to broaden their appeal, to soften their image. So it is that a fairly traditional, ideological conservative Republican from Denver, with a reputation as a political streetfighter, ushered in a new era for the Right.

Now Rove sits in the West Wing of the White House, with the title of The Senior Adviser to the President (note the definite article), rarely giving interviews or making public speeches, but having such a profound influence on events that he is widely acknowledged as the most important political figure in America, second only to his old friend. Although deferential to the President, their relationship thrives on banter. Rove contrasts their repartee with the sparkling wit of the TV programme West Wing. “Ours is rather childish,” he says, “and he gets the best of me every time.”

He adds that in the real West Wing “the lighting is nowhere near as flattering, there are no glass walls, and a lot less takes place in the hallway”.

“There has been nobody like Karl Rove in US political history,” comments Michael Barone, the respected author of the Almanac of American Politics, “nobody who has combined being policy adviser and political adviser to the President and combined an understanding of the substance of policy with an understanding of how to move the nation.”

Democrats concur. The former Clinton aide George Stephanopolous told The Times that “it is hard to imagine a presidential aide in modern times with a deeper involvement and deeper knowledge of both politics and policy than Karl Rove”.

Across Rove’s desk passes every major domestic policy decision awaiting the President — tax cuts, social security, Enron, campaign finance laws — and every vital political call the Republicans have to make. In the recent mid-term elections Rove not only had a big say in how Republican money was spent, he also called up potential candidates he thought might lose in tight Senate races and persuaded them to make way for more electable alternatives.

The stunning success of this manoeuvre has further increased Rove’s prestige, the currency that Washington trades in.

Rove’s true significance, however, owes itself to something else — to his understanding of the importance of ideas. The way he has helped George Bush and other conservatives to shape their message has not just powered Republican election victories, it also makes him relevant far beyond America’s borders.

Jim Pinkerton, an adviser to Ronald Reagan and the older George Bush, despaired of the latter’s lack of interest in domestic policy, and said so publicly. So he was surprised, when passing through Texas in 1995 promoting a book of ideas about public service reform, to be given red-carpet treatment by the former President’s son. Rove laid on a whole day of events for him, including an intimate lunch with the Governor.

Behaviour like this, repeated with many different people over many years, explains why, in Pinkerton’s words, “at one time or other every conservative intellectual in America thought Bush was listening to them”.