More than a year ago, Barack Obama came to the steps of the Old State Capitol in Springfield, Illinois to announce he was running for president. Saturday, he returned there to make a new announcement.

"Today I've come to Springfield to tell you that I've found a leader," said Obama. "A man with a distinguished record, a man with fundamental decency, and that man is Joe Biden."

Biden joined Obama on stage for the first time just 12 hours after he was officially named his running mate.

"Today in Springfield, I know my feet are in the right place," said Biden. "And I'm proud to stand firm with the next President of the United States, Barack Obama."

The 65-year-old has served in the U.S. Senate since 1972. He currently chairs the Senate Foreign Relations Committee. Democratic leaders say it's in that area where he can give Obama a boost.

"He has impeccable credentials on national security and foreign policy matters," said U.S. Representative Mark Udall (D) Colorado. "As a member of the Armed Services Committee, I want somebody like Joe Biden serving in the Vice Presidency."

But it's Biden's credentials that the McCain campaign is using to continue their message that Obama isn't ready to lead. A new ad launched shortly after the text messages were sent out shows a clip of Biden criticizing Obama's inexperience and another clip of him praising McCain.

"I would be honored to run with or against John McCain because I think the country would be better off," says Biden in that clip.

But standing united before a screaming crowd in Illinois Saturday, Obama and Biden say their new and strong partnership will lead them to victory come November.

"Joe Biden won't just make a good Vice President. He will make a great Vice President," said Obama.

"Ladies and gentlemen, it's time to elect Barack Obama President," said Biden.

Obama and Biden now look forward to the Democratic National Convention in Denver, which will begin Monday. Biden is slated to be the primetime speaker at the convention on Wednesday.