PHOENIX—Saying that it is time for change to come to Arizona, President Barack Obama on Tuesday formally announced that he will run for Senate against John McCain in the 2010 election.

Obama asks Arizona voters to send another message to Washington and John McCain.

Addressing a capacity crowd of nearly 72,000 at University of Phoenix Stadium, Obama stood before a giant banner emblazoned with his new "President Obama for Senate" logo—a basic facsimile of his 2008 campaign emblem with a cactus inscribed in the center—and called on voters to "turn the page and write the next chapter in the great Arizona story."

"I am, and always have been, motivated by a single, powerful idea: that I might one day play a small part in building a better Arizona," Obama said. "So I ask you today to join me in this quest. Our children, and our children's children, deserve it. Together, we can meet the challenges we face. Together, we can send a message to Washington, and together, we can beat John McCain."

"Yes, we can in Arizona," Obama continued to overwhelming applause. "Yes, we can in Arizona. Yes, we can beat John McCain. Yes, we can in Arizona."

Repeatedly throughout his speech, Obama labeled McCain as a Washington insider and criticized the 73-year-old four-term senator for being out of touch with everyday Arizonans. While acknowledging respect for his opponent's military record and years of public service, the president argued that being a decorated war veteran has little to do with improving Arizona's schools and putting its citizens back to work.

"Let me be clear: John McCain is a good man," Obama said. "He has served this state nobly for more than 20 years. But where was John McCain last year when the economy collapsed and the housing bubble burst? Was he here in Arizona looking out for families in need? Or was he crisscrossing the nation trying to further his own political career?"

John McCain meets with many of his supporters at a local Arizona diner.

According to Beltway observers, Obama's candidacy should come as no surprise. The 44th president has reportedly kept a close eye on McCain's poll numbers in Arizona, and launched a senatorial exploratory committee last November just hours after McCain confirmed that he would run for a fifth term.

"The key thing we learned in 2008 is that McCain is beatable," campaign manager David Plouffe said. "And our goal is to continue to exploit that, whether he is running for the Senate, mayor of Phoenix, or board president at an assisted living facility."

Obama has continued to keep pressure on McCain for months, most notably by befriending the senator's closest war compatriots, becoming a frequent commenter on daughter Meghan McCain's blog, writing a best-selling book entitled The One And Only House I Own, and sending flowers to McCain's wife on her birthday and anniversary.

Obama even made history in May by coauthoring the Obama-Feingold Act, a bill the president said "vastly improves" upon previous groundbreaking campaign finance legislation.

"My fellow Arizonans, we have an opportunity to do something special next November," Obama said. "With a strong ally in the White House, the issues that matter most to our state will finally be pushed to the forefront of Washington's agenda. Issues like economic recovery, immigration reform, and the simple satisfaction of watching a broken, elderly man realize that the one thing in life he could still cling to is no longer his."

Using the nearly $30 million in campaign fundraising leftover from his presidential bid, Obama has mobilized a massive grassroots movement on a scale never before seen in a Senate race. More than 400,000 volunteers have flooded Arizona since his announcement, and nearly 350 Obama campaign offices have opened throughout the state.

Early polls indicate McCain is leading by four percentage points. But Obama's numbers are expected to increase in the next 18 months, during which he plans to spend less time in Washington and focus his efforts on winning in Arizona.

According to constituents, the president's commitment may already be paying off.

"I've voted for John McCain in the last four elections, but I have to admit I'm intrigued by Barack Obama," Flagstaff resident Evan Casillas said. "I know John McCain. I like John McCain. He would probably continue to do well as senator. But that Barack Obama is awfully charismatic."

As of press time, McCain was not available for comment, as members of his Senate staff indicated he had left his office earlier in the day to take a long walk and clear his head.