Mr. Carmona, 62, is an untested candidate of vast experiences with a made-for-Hollywood biography. He was a high school dropout, born into poverty in New York City to Puerto Rican parents who struggled with alcoholism and drug abuse. He served in Vietnam, earning Bronze Stars, Purple Hearts and other combat decorations, and attended medical school before his eventual rise to surgeon general under President George W. Bush. He is running for public office for the first time, challenging a six-term congressman, Jeff Flake, 49, a Republican. Both are vying for the seat held by another Republican, Senator Jon Kyl, who is retiring. Though there is little reliable polling in the contest, both camps acknowledged that the race is closer than they expected in such a heavily Republican state. Beyond the balance of power in the Senate — enough states are in play that Republicans could regain the majority — the race carries enormous significance for Arizona, whose shifts in demographics threaten to upend its role as a Republican stronghold. Mr. Carmona was handpicked by President Obama to run for the Senate because of his résumé and his ethnicity, which could help galvanize the state’s Latino voters. The Democratic Party then cleared the field for him, sparing him primary attacks but depriving him of the chance to test his skills before the big fight. Mr. Flake, in the meantime, waged a feisty primary contest against Wil Cardon, a wealthy businessman who spent a small fortune on his campaign but lost by a considerable margin. Unlike Mr. Carmona, who often refers to himself as a “street kid,” Mr. Flake was raised on a ranch in Snowflake, a northern Arizona town named in part for his great-great-grandfather, the Mormon pioneer William J. Flake. Mr. Flake says he is “for limited government, economic freedom, individual responsibility and free trade,” tenets that have earned him staunch support from the Tea Party movement. He has also embraced issues of particular significance to rural voters, like environmental rules that he says have curbed the operation of coal plants, leaving many people unemployed and “devastating small-town economies.” From his campaign headquarters in Phoenix on Tuesday, where he was surrounded by young volunteers polling voters on the phone, Mr. Flake said, “I’m fighting to have some rational policy,” singling out the Forest Service and the Environmental Protection Agency as agencies that “need to be reined in.” Outside groups have been pouring money and resources into the state as the race has tightened. On Wednesday, FreedomWorks for America, a “super PAC” linked to the Tea Party, opened an office in Mesa. The operation at the heart of Mr. Flake’s base in suburban Phoenix will organize volunteers to solicit votes, said its executive director, Russell Walker, who flew in from Washington. On Tuesday, the Democratic Senatorial Campaign Committee bought $526,000 in airtime on behalf of Mr. Carmona, its first direct expenditure in the contest. (The committee had previously given $500,000 to the state’s Democratic Party to help pay for the campaign’s field offices, among other things.) The National Republican Senatorial Committee has donated $500,000 worth of ads to the Flake effort. Mr. Carmona, a longtime independent, is running as a Democrat. That is not because the party is “a perfect fit,” he said, but because “I was forced to pick a position, and when I looked at where the Republicans were, especially in this state — immigration, women’s issues — I chose the Democratic Party.” He has nonetheless tried to stitch together what he has taken to calling “a coalition of reasonable people” to carry him to victory. He has focused on constituencies long believed to be Republican stalwarts, like veterans, who make up roughly 15 percent of eligible voters in the state, and seniors, many of whom dislike the Medicare plan proposed by Representative Paul D. Ryan, the Republican vice-presidential nominee. Mr. Carmona has also appealed to women who are unhappy about the state’s attempts to curb reproductive rights. All along, though, Mr. Carmona has courted Latino voters. He released his second Spanish-language commercial on Tuesday, which introduces him as “uno de nosotros” — one of us — while highlighting Mr. Flake’s vote against the Dream Act, which would have given certain immigrants brought to the country illegally as children a path to legalization. Mr. Flake has begun to make his case to Latinos as well. He has started running his first Spanish-language ad on television and radio, trying to tap into whatever anti-Obama sentiment there is in that community by referring to Mr. Carmona as “el hombre de Obama” — Obama’s man. A combination of factors, including the state’s legislative push to curb illegal immigration and the presence of a Hispanic candidate like Mr. Carmona in the race, — have been galvanizing among advocacy groups in Arizona, triggering the largest Latino voter registration efforts in memory. Still, Tara Blanc, a lecturer at the School of Public Affairs at Arizona State University who has studied Latino voting patterns in the state, said Latinos tended to be poorer, younger and less educated than the rest of the population. Those factors generally contribute to low turnouts, she said, so “whether they’ll go to the polls is anybody’s guess.” Their transformative power lies, most likely, in the future. By 2030, Latinos are expected to make up 25 percent of all registered voters in Arizona, up from 15 percent in 2010, according to an analysis by the Morrison Institute for Public Policy at Arizona State. Chip Scutari, who runs a bipartisan political consulting firm in Phoenix, said a Latino on the ballot could be “the tipping point for the Latino vote.” But, he added, the state has “a lot of conservative, pro-life Latinos,” who are more likely to vote Republican. “To say the Latino vote will automatically go to Democrats,” Mr. Scutari said, “is oversimplifying the situation.”
