Barack Obama takes office today with a realistic prospect of joining the ranks of history's most powerful presidents.

The more familiar observation, that he confronts daunting trials, enhances that prospect. Emergencies have always brought commensurate new authority for the presidents who faced them, not only because the public demanded action but also because rival branches of government went along.

Obama arrives with a rare convergence of additional strengths, some of them inherited and some of his own making. Predicting a presidency, to be sure, is hazardous business, and much will depend on Obama's choices and fortune. But historians, recent White House officials and senior members of the incoming team expressed broad agreement that Obama begins his term in command of an office that is at or near its historic zenith.

"The opportunity is there for Obama to recast the very nature of the presidency," said Sean Wilentz, a presidential historian at Princeton. "Not since Reagan have we had as capable a persuader as Obama, and not since FDR has a president come in with quite the configuration of foreign and domestic crises that open up such a possibility for the reconstruction of the executive."