Calderón´s ascension marks the first time in more than a century that a political force other than the once-dominant Institutional Revolutionary Party (PRI) passes the torch to a successor after a democratic election.

Calderón follows fellow National Action Party (PAN) member Vicente Fox, who broke the PRI´s seven-decade grip on power in 2000.

Fox´s inauguration, six years ago to the day, was accompanied by much fanfare and a heady atmosphere of hope.

But Fox left office Friday at one second after midnight under a cloud of disappointment, leaving behind a nation as wracked by poverty as when he took office.

Some 103 foreign delegations are in the nation´s capital for the swearing-in ceremony, as are 1,900 accredited foreign press correspondents. They will be joined by more than 600 senators and deputies, and protected by several thousand troops from the Federal Preventative Police, the Navy, and Federal District law enforcement officials.

Thousands more, including defeated candidate Andrés Manuel López Obrador, will fill the Zócalo Friday morning to protest Calderón´s inauguration.

None of those diverse participants, however, could be sure Thursday night exactly what was going to happen at the swearing- in ceremony, scheduled to take place before a joint session of Congress beginning at 9:30 a.m. on Friday in the Legislative Palace of San Lázaro.

Legislators from the PAN and the opposition Democratic Revolution Party (PRD) continued their occupation of the speakers´ platforms Thursday night, and neither was giving any indication it would clear out in time for Calderón to take the oath of office.

After more than five hours of negotiations, party leaders were unable to break the impasse and the protesting legislators were preparing to spend another night sleeping in the Chamber.

Party leaders and Chamber President Jorge Zermeño had hoped to work out a deal whereby the legislators would vacate the floor of Congress, but it was unsuccessful.

The PRD and Labor Party even voted against a motion to convene Friday morning´s joint legislative session, so there was little hope that continuing the talks would produce a settlement.

Zermeño told reporters that he would continue looking for a way to win full consensus, but EL UNIVERSAL reported that no further talks were planned.

The PRD, which considers Calderón´s election victory fraudulent and his assumption of the presidency a usurpation, has promised to disrupt the ceremony if it takes place in the Chamber of Deputies hall.

PRD legislators successfully prevented Fox from delivering his final State of the Nation Address on Sept. 1 by storming the speakers´ area, so the Senate and Chamber of Deputies leadership, as well as the Calderón transition team and the Fox administration, have taken the threat seriously.

Pending a late change of plans, legislators and potential attendees were assuming the event would take place in the Chamber as planned, albeit under especially heavy security.

The lower house´s social communications department released an agenda Thursday indicating the session would start at 9:30 a.m. in the Chamber, with Fox arriving at 10 and Calderón shortly after to take the oath of office.

But Calderón was set to meet with Fox late Thursday night in the presidential residence of Los Pinos for a transfer of power ceremony, which would include activating Calderón´s Cabinet.

Legal experts agree that Calderón´s presidency kicks in at one second after midnight on Dec. 1, but that he still must take the official oath of office, as every public official is required to do.

What´s unclear is whether that oath must be administered before a quorum in Congress, and what happens if the ceremony is prevented from taking place there.

Fox and Calderón repeated Thursday that they will both be present at the Chamber Friday morning - Fox to bequeath the presidential sash and Calderón to take the oath of office.

Two heads of state - Peru´s Alan García and Ecuador´s Alfredo Palacio - cancelled their visits to Mexico. Both cited scheduling conflicts.