BRUSSELS — At long last, Gordon Brown is taking over from Tony Blair as Britain's prime minister, thus attaining his lifelong ambition, as if by right. That is his first problem. He has not been elected by anyone — not by the Labour Party, and not by Britain's voters; he has merely come into an inheritance that he has long thought was his due.

How, then, will Brown acquire legitimacy as Britain's new leader? The one thing that is clear is that he will not gain legitimacy if he offers only more of what Blair has been dishing up for the past 10 years.

Brown's second problem is the mirror image of the first. As a senior member of Blair's government throughout its tenure, he shares responsibility for everything that Blair has done. Political commentators sometimes claim to detect important differences in their underlying political attitudes. However, in practice, Brown has remained in the shadows, skillfully managing the economy, but remaining silent and enigmatic on vital political issues, and apparently endorsing everything Blair did.