Obama is expected to deliver remarks at a fundraiser in the southern Arizona city on Monday evening as part of a four-state campaign push in the West, with other stops in Colorado, Nevada and New Mexico.
Her visit comes on the heels of stops in Arizona last week by Vice President Joe Biden and presumptive Republican nominee Mitt Romney.
Biden attended a private fundraiser on April 19 in Phoenix. The day after, Romney had a round-table discussion with Phoenix-area Hispanic business and community leaders before holding a rally in Tempe.
"All the indicators are that Arizona's in play," said Jim Haynes, president of the nonpartisan, Phoenix-based Behavior Research Center, which conducts election polls.
"The voters are obviously restless and wrestling with what they're going to do in November," Haynes said. "There's still a lot of question marks in their minds. And as things unfold positively and negatively on behalf of each one of them, I think people are going to bounce back and forth."
A recent poll by the Behavior Research Center showed that 42 percent of the 511 registered voters contacted across the state supported Obama, that 40 percent supported Romney and that 18 percent were unsure. Because the poll, conducted April 9-17, had a margin of error of plus or minus 4.4 percentage points, Obama and Romney are considered about even among Arizona voters.
In terms of fundraising, Romney has been more successful, raising $1.7 million in the state through March 31, compared to Obama's $1.1 million.
Haynes said that although Arizona doesn't carry the electoral punch like California, Florida and other states, it is highly coveted by both parties for its national reputation as a Republican stronghold and as ground zero for the immigration debate.
"Arizona's a symbolic state now, for both sides," he said. "It's big stuff for a Democratic candidate to be able to say, `I'm running neck and neck in a state like Arizona.' The flip side is that Romney has a strong interest in keeping the so-called faith base safe.
"We're going to get a lot of attention paid to Arizona," Haynes added.
The last time a Democratic candidate won the presidential race in Arizona was Bill Clinton's re-election in 1996.
Shane Wikfors, communications director with the Arizona Republican Party, said the Obama campaign is well-organzied and has a network in place in Arizona and across the country, giving them an advantage.
But Wikfors said Romney's campaign is very disciplined and can come out on top.
"Our take on the Obama administration thinking that they can put Arizona in play is, let them continue to believe that," he said. "In fact, let them spend as much money here in Arizona as they want. Arizona is going to remain red."
He said Arizonans upset about the economy and the unemployment rate will vote for Romney.
Luis Heredia, chairman of the Arizona Democratic Party, said Democrats have thought they could win presidential races in the past but that there is a different energy on the ground in the state this time around.
He said Arizonans frustrated with the Republican-led Legislature will turn to Obama, and that the first lady's visit Monday should be the first of many high-profile visits from Obama's team.
"It's going to motivate Democrats for what's going to be an exciting summer," he said. "We're hoping her visit will be the first of many different things that will motivate voters, not only Democrats, but Independents and frustrated Republicans."