35. Obama-Biden it is !

from CNN, Springfield, Illinois

Presumptive Democratic presidential nominee Barack Obama introduced Sen. Joe Biden to the nation as his running mate on Saturday, telling supporters he is "a leader who is ready to step in and be president."

"For months, I've searched for a leader to finish this journey alongside me and join me in making Washington work for the American people. I searched for a leader who understood the rising costs confronting working people and will always put their dreams first," Obama said.

"Today, I've come back to Springfield to tell you I've found that leader," he said.

The rally is the pair's first joint appearance since Obama announced that Biden, the senior U.S. senator from Delaware, would be his running mate on his Web site and in a text message to supporters early Saturday morning.

Thousands of cheering supporters gathered Saturday for the rally in Springfield, Illinois, where Obama announced his candidacy last year. It will be their only public appearance together before next week's Democratic convention in Denver.

As he took to the podium at Saturday's rally, Biden invoked the 16th U.S. president, Abraham Lincoln, who was from Illinois.

"President Lincoln once instructed us to be sure to put your feet in the right place and then stand firm," said Biden, a native of Scranton, Pennsylvania.

"Today in Springfield, I know my feet are in the right place, and I'm proud to stand firm with the next president of the United States of America, Barack Obama."

Democrats hope that Biden's working-class roots and foreign policy experience will help Obama, who informed Biden of his decision Thursday.

Sen. John McCain, the presumptive Republican nominee for president, called Biden on Saturday morning and congratulated him, CNN's John King reported.

Before the text messages were distributed, multiple Democratic sources confirmed to CNN early Saturday that Obama wanted the Delaware senator as his vice president.

On Friday, CNN learned that three Democrats who had been considered contenders for the No. 2 spot, New York Sen. Hillary Clinton, Indiana Sen. Evan Bayh and Virginia Gov. Tim Kaine, had been ruled out.

"Sen. Obama has continued in the best traditions for the vice presidency by selecting an exceptionally strong, experienced leader and devoted public servant," Clinton said in a written statement Saturday morning.

"Sen. Biden will be a purposeful and dynamic vice president who will help Sen. Obama both win the presidency and govern this great country."

Biden's stock rose this week after he returned from a two-day trip to the Republic of Georgia after Russian troops invaded.

Biden, chairman of the Senate Foreign Relations Committee, brings decades of experience that could help counter GOP attacks on Obama's lack of experience in foreign policy.

McCain's campaign quickly reacted to word that Biden would be Obama's running mate, calling attention to Biden's past comments about Obama's experience.

"There has been no harsher critic of Barack Obama's lack of experience than Joe Biden," McCain campaign spokesman Ben Porritt said in a written statement.

"Biden has denounced Barack Obama's poor foreign policy judgment and has strongly argued in his own words what Americans are quickly realizing: that Barack Obama is not ready to be president."

In a debate during the Democratic primary contest, Biden raised questions about other candidates' foreign policy experience.

"Who among us is going to be able on Day One to step in and end the war? Who among us understands what to do about Pakistan? Who among us is going to pick up the phone and immediately interface with Putin and tell him to lay off Georgia because Saakashvili is in real trouble. Who among us knows what they're doing? I have 35 years of experience," Biden said.

During another debate, moderator George Stephanopoulos referred to some of Biden's comments on Obama.

"You were asked, 'Is he ready?' You said, 'I think he can be ready, but right now, I don't believe he is. The presidency is not something that lends itself to on-the-job training,' " Stephanopoulos said.

"I think I stand by that statement," Biden replied.

In July, Biden said he would choose Obama's judgment over McCain's war record and foreign policy experience.

"But 20 years of experience that has not been very solid in terms of projecting what was going to happen just doesn't make you a better commander in chief," Biden said. "We don't need as a commander in chief a war hero. John's a war hero. We need someone with some wisdom."

Biden abandoned his own White House run after a poor showing in Iowa's first-in-the-nation caucuses. He also ran for the 1988 Democratic presidential nomination but dropped out after charges of plagiarism in a stump speech.

Biden was first elected to the Senate in 1972. Shortly afterward, his first wife and daughter were killed in a car accident. He considered resigning but decided to continue with his political career.

Biden is serving out his sixth term, making him Delaware's longest-serving senator.

He is married and has three children. He received his undergraduate degree from the University of Delaware and got a law degree from Syracuse.

In 1988, Biden suffered an aneurysm and nearly died but has recovered fully.

One of Biden's grandfathers was a Pennsylvania state senator, according to the Almanac of American Politics.

Biden will make his first big speech as the vice presidential candidate on Wednesday, the third night of the Democratic convention.