President-elect Barack Obama, tracing the train route Abraham Lincoln took nearly a century and a half ago, undertook the final leg of his inaugural journey to the nation's capital on Saturday, pledging to reclaim America's spirit but also warning of steep challenges facing the country.

"Starting now, let's take up in our own lives the work of perfecting our union," he said at Philadelphia's historic 30th Street train station.

"Let's build a government that is responsible to the people and accept our own responsibilities as citizens to hold our government accountable. ... Let's make sure this election is not the end of what we do to change America, but the beginning and the hope for the future," he said.

While talking about the future, Obama reflected on the past, echoing the words of the Declaration of Independence, Lincoln and President John F Kennedy. He cited the founding fathers who risked all without assurance of success in Philadelphia in the summer of 1776.

"They were willing to put all they were and all they had on the line — their lives, their fortunes, and their sacred honor — for a set of ideals that continue to light the world. That we are equal. That our rights to life, liberty, and the pursuit of happiness come not from our laws, but from our maker. And that a government of, by, and for the people can endure," Obama said.

It was a momentous day for the Obamas. And for Michelle Obama, it was also time to celebrate her 45th birthday.

The president-elect's triumphant day — a time to be heralded by cheering throngs along the 137-mile rail route — was starting in Philadelphia with a sober discussion of the country's future with 41 people he met during his long quest for the White House.