MEXICO CITY — What Felipe Calderon lacks in charisma, he makes up for with determination. And that may be what it takes to govern Mexico.

On Friday, the stiff, bespectacled career politician strode into the chaos of a congressional chamber filled with whistling and brawling lawmakers. Maintaining a focused, almost serene demeanor amid the catcalls and hostility, he held out a steady hand and took the oath to be Mexico's president.

In an appearance that lasted just four minutes, Calderon stared down the opposition and sent a powerful message to a divided nation: This president won't back down.

"It was good action," said California Gov. Arnold Schwarzenegger, who watched from the balcony.

Later, in his first speech as president at the National Auditorium, Calderon asked for a chance to win over tens of thousands of protesters massing outside but warned he wouldn't let them stall his government.

The 44-year-old lawyer with a masters in public administration from Harvard demanded a strict rule of law with no tolerance for the violent protests, drug wars and kidnappings that have tarnished Mexico's reputation and prompted Washington to warn U.S. citizens against traveling south of the border.

"Laws must protect citizens, not criminals," Calderon said. "It won't be easy or quick. It will take time and a lot of money. But rest assured: This is a battle that I will lead."

It was an impressive start, far different from his predecessor Vicente Fox, Mexico's first opposition president in 71 years, who seemed to do all he could to avoid conflicts.

The ceremony in congressional chambers where banners labeled Calderon a "traitor to democracy" was a stark contrast to the national euphoria that ushered Fox into office six years ago. But in many ways, Calderon seems more likely to succeed as president than the charismatic cowboy he replaces.

Fox rode into power on a wave of jubilation over the possibility that Mexico could truly change after decades of authoritarian, one-party rule by the Institutional Revolutionary Party, or PRI. But Fox largely disappointed voters who believed his promises of millions of new jobs and prosperity. Calderon is from the same National Action Party as Fox.

Calderon faces monumental challenges: The nation remains polarized over his narrow victory in July 2 elections. His chief rival, Andres Manuel Lopez Obrador, has declared himself Mexico's "legitimate" president and set up a parallel government.

On Friday, Lopez Obrador said he would never recognize Calderon's presidency. "I won't respect a thief, and I will always call him that," Lopez Obrador said.

But Calderon is a savvy veteran of Mexico's Congress with a host of advantages over Fox, who came in as an outsider. His National Action Party has the largest number of congressional seats and has formed an alliance with the PRI that nearly guarantees quick approval for any reforms he proposes.

The economy is on track for its fastest expansion in six years with 4.8 percent projected growth, and the country is close to creating nearly a million jobs this year thanks to a boom in the construction and retail service industries. Calderon has touted jobs as the solution to alleviating poverty.

"Instead of leaving to work in the United States, I want to look for investment here in Mexico for our workers," Calderon said.